Why Did the US Enter WW1: 10 Reasons to Explain History’s Most Important Military Intervention

Why Did the US Enter WW1: 10 Reasons to Explain History’s Most Important Military Intervention


The First World War, to put it bluntly, was an absolute waste. It resulted from the unworkable entanglement of a barbed web of European alliances, a series of catastrophic diplomatic disasters, and a chauvinistic and utterly vacuous display of the ‘my dreadnought battle cruiser’s much better than yours’ ilk from two of the world’s leading superpowers. Most disheartening of all, though, was that the war was as inevitable as it was pointless.


The war began on 28 July 1914, yet it would not be until 6 April 1917 that the US came to the aid of the Allies. This historical curiosity requires some explaining. Firstly, the incumbent president Woodrow Wilson seemed to be taking George Washington’s ‘why quit our own to stand upon foreign ground’ mantra as gospel. The son of a Presbyterian, and a man whose academic background shaped his personal philosophy of pacifism, Wilson advocated a position of isolationism and neutrality ‘in thought and deed’. Secondly, there was little appetite for war among America’s immigrant population; Irish, German and Swedish Americans had little to gain from getting involved in the struggles of their ancestral countrymen and far less to gain from creating new frictions in the new largely world.


Lack of volition, therefore, explains why the US took so long to join the war. But it does not explain why, after so many years of staunch adherence to a policy of neutrality or, at best, preparedness, the US finally entered. This articles has compiled a thematically complete list of reasons to explain the US’ intervention. It can’t claim to be comprehensive, but hopefully it will provide the lay reader with a solid overview, and the specialist with some interesting and previously unknown information.

10 The ‘Rape of Belgium’

Belgium was being raped.

Belgium’s strategic position made her vulnerable from the war’s outset. Germany’s military blueprint – the highly intricate Schlieffen Plan – had established that if Germany were to win the war, she would have to quickly defeat France in the west, before Russia could mobilize in the east. To do this, the bulk of Germany’s army would pass through Belgium and Luxembourg, circumventing France’s eastern border fortresses before making its way down and encircling Paris. What the Germans hadn’t expected was that Belgium would remain neutral and refuse her military access.


Germany’s answer was to invade Belgium, which she did on 4 August 1914, drawing Britain into the war. The invasion was brutal, as even the chief of the German general staff, General Helmuth von Moltke, would admit: ‘Our advance into Belgium is certainly brutal, but we are fighting for our lives and those who get in the way must take the consequences.’


The problem was that many of the 5,521 killed between 4 – 28 August were unquestionably non-combatants who didn’t ‘get in the way’. Though the Germans claimed to be targeting francs-tireurs (snipers), Women and children and the elderly increasingly featured among the dead, and the modes of execution were indefensibly heinous – in one case residents were executed 10 at a time, the last having to climb upon a mound of the dead before being shot. The atrocities committed by the Germans towards the Belgian citizenry were enough to earn international censure, though what must have particularly affected the US was that Belgium had tried to remain neutral. German actions in Belgium were appalling, but there was one case above all others that stood out and shocked the world.

9 The razing of Leuven

Leuven was razed.

Anton_Ivanov / Shutterstock.com

The Germans first occupied the Belgian city of Leuven on 19 August, a few days into the main German force’s advance. At first, the occupation was not marked by any particular violence. A tragic series of events 6 days later on the 25 August, however, would change all that. Belgian forces arriving northwest of the city from Antwerp launched an initially successful attack on German forces, routing them into the city of Leuven. The occupying German forces mistook them for allied invaders, and in the confusion friendly fire was exchanged. When the smoke had settled, blame was not laid at the feet of the German command but at Leuven’s citizenry who were accused of contriving the confusion.


Intending to make an example of Leuven and so discourage further potential insurrection, the Germans set about on the city’s complete destruction.

German soldiers killed 209 citizens, burned down around 1,100 buildings – including the university library which saw the loss of 230,000 books, – and displaced some 42,000 people: the city’s entire surviving population.


As with all other German atrocities that made up the ‘Rape of Belgium’, razing Leuven served absolutely no strategic purpose. All it did, as we’ve already established, was mobilize public opinion against the Germany and the Kaiser; particularly in the US. Leuven’s symbolism was particularly potent; burning books did untold damage to Germany’s cultural predominance (established in the 18th century Enlightenment) and enabled the European intelligentsia to portray the Germans as waging a war on culture.

8 The sinking of the Lusitania

The Lusitania was lost.

Though many British ships were called into military service during the war to replenish substantial U-Boat losses, the R.M.S. Lusitania – sister to the similarly ill-fated R.M.S. Titanic – kept to her traditional transatlantic route. Transporting 1,959 civilians, along with substantial cargo and munitions, the Lusitania departed from New York on 1 May 1915 amongst a deserved air of agitation; the German embassy in Washington had issued its threat to sink any vessels traveling in British water during the state of war.


The Germans were proving true to their word. On 6 May, the day before the Lusitania’s sinking, the German submarine U-20 sank two 6,000 ton British vessels. Lusitania’s captain took suitable precautions but it was not enough. At 13:20 on 7 May U-20 sighted Lusitania, and at 14:10 it fired a single torpedo. The ship took on water fast, and within minutes was leaning so far to the starboard side that launching the lifeboats went from being a herculean to an impossible task. The Lusitania sank in just 18 minutes, in freezing waters 11.5 miles off the south coast of Ireland.


Of ship’s 1,959 total, 1,195 perished with the Lusitania. Moreover, only 11 of the 139 US citizens on board survived. This drew international outrage, not just because of the number of losses but also because of the illegality (maritime law required the safe passage of passengers aboard civilian ships). It also plunged German-American relations into crisis, and contrary to Roosevelt’s protestations, war was only averted because of Germany’s promise to respect the US neutrality. For now…

7The execution of Edith Cavell

Memorial to Edith Cavell

The first notable female casualty of the war was a British nurse, Edith Cavell. As well as providing aid to the wounded of both sides, Cavell’s organization had been helping some 200 allied soldiers trapped behind enemy lines after the Mons campaign in Belgium return to Britain via Holland. According to German military law, harboring enemies was a crime punishable by death and Cavell was arrested on 3 August 1915. The British were unable to protect their nurse, and after several interrogations she was handed her sentence. At 7:00 on 12 October, Cavell was executed along with four other Belgians by firing squad at the Tir national shooting range in Schaerbeek, Belgium.


The Germans claimed that Cavell had been a spy; something vehemently denied by the British but, in light of recent evidence, probably not without some truth. Regardless, Cavell’s execution was exploited particularly by the British, who used her as a vehicle for their propaganda. Books, newspaper articles, pamphlets, and images began to circulate detailing Cavell’s tragic case. But her legacy was not only felt amongst the allies on the continent. We can attest to the effectiveness of allied propaganda across the Atlantic by the fact that a version of Edith Cavell’s story was published in the American Journal of Nursing. I say version, because what was reported was as counterfactual as it was moving; Cavell was said to have fainted after refusing to face the firing squad blindfolded, to which the German officer’s response had been to walk up to her and shoot her in the head.

6 To fight against tyranny

The Germans were committing unforgivable atrocities.

One particular episode stands out from the arrival of John J. Pershing’s expeditionary force in France (June – July 1917). On a detour to the tomb of the Marquis de Lafayette on 4 July, Pershing’s aide, Colonel Charles E. Stanton, uttered the remark: ‘Lafayette, nous voilà’ (Lafayette, we are here).


The figure evoked had considerable significance in American history. Lafayette, a French aristocrat, had bucked the trend among his European milieu in helping American revolutionaries liberate themselves from the British yoke in 1781. Now, as alluded to by Stanton, the Americans had come to liberate Europe from a Teutonic yoke of its own.


When looking back at the First World War, especially through the distorting prism of the Second, it is tempting to view American intervention on the side of the allies as a given. But we should not fall into the trap of conflating hindsight with inevitability. The Central Powers were not alone in committing atrocities: Russian treatment of civilians in the East matched anything perpetrated by the Germans in Belgium of France, and the British army, it has recently been suggested, largely tolerated the killing of German POWs. The difference was that the Allies exploited their propaganda much more effectively than their Axis enemies. The Rape of Belgium, the sinking of the Lusitania and the execution of Edith Cavell all provided structure for a narrative of German barbarism; filled in with other aspects of German unconventionality (the use of Zeppelins and mustard gas). There were, of course, fabrications intended to shock the US out of neutrality. Some were identified and outlined, as in a 1929 article in The Nation. But the end result was the same: when the US arrived in 1917, they had named their tyrant.

5 German espionage

The Germans were spying.

The most important munitions depot in the US during the war was ‘Black Tom’ in New Jersey. It was here that US-produced munitions were stored before being shipped across the Atlantic to the Allies (owing to the British naval blockade, the Germans were excluded from purchasing US munitions). Black Tom facilitated a considerable storage capacity; the National Dock and Storage Company had built warehouses and depots on a pier that stretched over a mile long. Indeed, prior to the explosion, Black Tom was believed to have been holding around 1,000 tons of small arms and artillery ammunition.


In the early hours of 30 July 1916 a series of explosions began to gut the island, the most powerful causing an earthquake measuring 5.5 on the Richter scale. The presence of substantial amounts of TNT, shrapnel, black power and dynamite amongst the munitions substantially added to the severity of the explosions which killed between five to seven people, including a 10-week old baby over a mile away who was flung from its crib.


Black Tom was the most costly manmade disaster in American history, with final damages reckoned to be somewhere in the region of $20 million. It was not, however, the only case of German sabotage and espionage. The German saboteurs and naturalized American citizens contemporary investigations found to be responsible, Kurt Jahnke and Lothar Witzke, had already been implicated in the explosion at San Francisco’s Mare Island Naval Shipyard in March 1917. Together with a number of other homeland attacks attributed to espionage, the cumulative effect of this growing suspicion slowly turned the tide of American sentiment against Germany.

4 The Zimmermann Telegram

The Germans were conspiring. With Mexico?

Named after its architect, the German foreign secretary Arthur Zimmermann, the Zimmermann Telegram was a coded message sent by the German Foreign Office in January 1917 proposing a German-Mexican alliance and an increase in Mexico’s territory if the US entered the war. British intelligence intercepted and decoded the message immediately but waited until 19 February to pass its contents on to the Edward Bell, secretary of the US Embassy in London. In waiting, they were hoping to capitalize on growing American anti-German sentiment and therefore make the telegram’s revelation particularly effective in galvanizing the US into war.


The timing of the revelation was, at it happened, particularly inauspicious for the Germans. Wilson learned about the telegram’s contents on 24 February – the day before he was to address congress and request that they arm US merchant vessels against German U-Boats. Moreover, on the same day as the congressional address another passenger ship was sank, the R.M.S. Laconia, drowning two American women.


When the Zimmermann Telegram’s contents were published on the front pages of the American press on March 1, public opinion was initially divided. Some were incredulous, believing it to be a fake; others, most prominently Roosevelt, believed it provided justification for war. Ultimately, Zimmermann’s admission to the document’s veracity on 3 March, combined with the sinking of a further three American merchant ships on 15 March, irrevocably turned opinion against Germany. The ships had been sunk in the German campaign of unrestricted U-Boat warfare, and it is to this subject that we now turn.

3 Germany’s resumption of their unrestricted U-Boat campaign

German u boats were sinking everything.

The sinking of the Lusitania in May 1915, although straining for German-American diplomatic relations, had not been disastrous. Much to the Allies’ ire, Wilson didn’t consider it a pretext for entering a war the country was not ready to fight. He did, however, issue an ultimatum saying that further contravention of maritime law affecting Americans would be considered ‘deliberately unfriendly’.


Such contravention was not far off. On 19 August, U-24 sank the S.S. Arabic, killing 3 Americans and obliging Germany to issue the Arabic Pledge on 18 September, allowing civilians safe passage from a passenger ship before it was sunk. On 24 March 1916 the Germans reneged, sinking the S.S. Sussex without warning and killing three Americans. Wilson issued Germany a final ultimatum: break off unrestricted campaign U-Boat warfare or diplomatic relations would cease. Germany, eager to keep the US out of the war, had little choice. They agreed to the terms in the Sussex Pledge (4 May 1916).


Not all in German command, however, were on board with this. Chief Admiral Henning von Holtzendorff repeatedly emphasized the necessity of depriving the Allies of their supplies if Germany were to win the war, and advocated, in December 1916, that the U-Boat campaign could be restarted and the war concluded before the US’ entry. German command accepted, and on 1 February 1917 the campaign was resumed. Further loss of American life over the following months gave Wilson no choice, and on 2 April Wilson called upon congress to ‘accept the status of a belligerent which has thus been thrust upon it’ and to declare war on Germany. Four days later, congress accepted, and the US entered the First World War.


There was money to be made.

As war was breaking out in Europe, the US was reaching the end of a severe economic recession that had gripped the country since 1913. The newly reinvigorated US economy was able to capitalize on European militarism, substantially increasing its exports, awarding more than $3 billion worth of contracts – through the mediation of commercial giant J.P. Morgan – from the British and French governments to American businesses, and extending credit to the Allies that averaged around $10 million a day.


To say that financing the war oiled the engines of American industrialization and modernization would be an understatement; the US’ GDP increased by around 20% throughout the war, and her industrial production by a staggering 32%. However, the enormous investment the US had made in the Allies – especially compared to the Axis powers – was as political as it was financial. Allied defeat could result in the defaulting of debts which by this stage exceeded some $2 billion as opposed to Germany’s $27 million, and uncomfortable as it may seem, economic factors such as these not only influenced the US’ decision to go to war, it influenced their decision about who to go to war with.


At many stages of the war, there was little love lost between the US and Britain. As things were cooling off with Germany in 1916, relations became strained with the British over their harsh repression of the Irish Easter Rising and their boycotting of US companies engaged in trade with Germany. German U-Boat campaigns, the intercepted Zimmermann Telegram and a healthy dollop of allied propaganda eventually dictated the decision, but it was at no stage a given.

1 It would be ‘the war to end all wars’

We were naive.

The sheer scale of the First World War – in terms of human involvement, loss, geographical dispersion, technological consumption and, conversely, technological progress – would probably remain incomprehensible to this day had it not been for the Second. It was apocalyptic, all encompassing and, as harkened on about by various governments partly out of conviction and partly out of morale-boosting propaganda, never to be repeated. It was ‘the war to end all wars’.


The phrase – commonly attributed to Wilson, though he only used it once, – was first coined by the British author H.G. Wells, who published a collection of articles under the title The War That Will End War in 1914. Wells saw the war as the only possible way to bring peace to a world gripped in the clutches madness.


To each group, ‘the war to end all wars’ meant something different. To the enlightened liberals, it was a means to establish the conditions for freedom and democracy. To those living under colonialism, it was a first step towards more rights or even independence. Tragically, to those focused on ethnic purification, it meant giving license to abhorrent acts of genocide. To those on the frontline, it would become something of a catchphrase, uttered, one presumes, increasingly in the hope that no future generation would have to go through something so horrific. The phrase’s Wilsonian incarnation perfectly reflected the philosophy of the man uttering it. His 14 points, outlined towards the war’s conclusion in 1918, reflected his determination that a war of this kind should never be repeated. Regrettably, Santayana’s riposte (‘only the dead have seen the end of war’) was to stand up better to the test of history.



The US’ intervention, despite providing the conditions that allowed Russia her revolution and removal from the war, undoubtedly hastened the war’s end. By 1918 the collapsing Central Powers were coming to the realization that they could not compete for manpower with the arrival of potentially millions of new ‘doughboys’ – as American recruits were affectionately called – in Western Europe. After the allied counterattack to Ludendorff’s failed Spring Offensive of 1918, morale completely collapsed among the German military and domestic population. The Kaiser’s abdication was soon to follow, as was signing of the armistice of 11 November 1918 which formally concluded the war.


Unfortunately, in the years to follow it became increasingly apparent that the Wilsonian vision of a post-war world, instead of being illuminated by the light of liberty and democracy, was to be clouded by the darkness of extreme nationalism, proletarian-utilitarian autocracy in Russia, and anti-democratic governments in Central Europe. ‘The war to end all wars’ had carried the right sentiment. It was the harsh terms of the peace, however, that sowed the seeds for Second World War’s outbreak in 1939.


Returning to the immediate aftermath, America emerged from the war the clear victor. Its army had expanded exponentially to number around 5 million, while its losses – compared to those of the European armies – were very few. This is not to say, of course, that 116,000 losses is insubstantial, but the figure becomes rather more sobering when compared to France’s losses of between 156-162,000 during the Battle of Verdun, or Britain’s losses of 19,250 on the first day of the Somme alone. The military was not the only section of American society to experience unprecedented growth. In almost all respects, the US prospered in the post-war years. But it was her unquestionable economic dominance – now greatly overshadowing that of the exhausted former European powers – that announced her arrival onto the world stage.