Growing up in Australia I only ever learnt about the diggers and of Gallipoli, and sometimes of Britain’s involvement. I’ve always wondered wether America had a role in the First World War, and if so, what was it? Did they join the war immediately, or not until later on like in World War Two? What were their motives for joining the war?
Hi there, welcome to our community.
There's a few questions here so let's address them one by one and in an order that
The US did not declare war on Germany until 2 April, 1917 and then not on Austria-Hungary until December of that year. The reason for the United States late entry into the war is the persistent desire to remain neutral during the conflict until circumstances pushed the US President Woodrow Wilson to ask Congress to declare war on Germany.
Pro-neutrality forces in the United States included the clergy, Irish-Americans and German-Americans. The two aforementioned ethnic groups were either anti-British or pro-German and both had significant enough influence in US society to influence public opinion regarding America's stance in the war. However, circumstances between 1914 and 1917 had drastic impacts of US public opinion that shifted it towards the Entente and away from Germany. In particular, German atrocities in Belgium cast the nation as the bad guy in the conflict and Germany's policy of unrestricted submarine warfare saw the sinking of many ships that either had US sailors or civilians on board. The most notable of these was the sinking of the Lusitania off the coast of Ireland in 1915 which claimed 128 American lives.
The final nail in Germany's diplomatic coffin was the Zimmerman Telegram. In 1917, the German Foreign Secretary Arthur Zimmerman dispatched a coded telegram to Mexico requesting a Mexican declaration of war on the United States. It was hoped that such an act would divert US attention and resources, preventing the US from intervening in Europe. However, the British intercepted the message and passed it on to the United States who, naturally, were not impressed. Such a souring of both public and diplomatic relations eventually culminated in Wilson's request to Congress for a declaration of war.
(Part of this answer is taken from a previous comment of mine on an older post)
Despite their declaration of war, the United States was a long way from being able to contribute to the war effort in Europe. The US Army was small and relatively inexperienced (especially in regards to the type of warfare being fought on the Western front). The Army would require a massive expansion prior to deployment and it would take time. However, by May of 1918, more than a million US troops had arrived in France and were making their way to the front. There impact on the frontlines is debated as by the time of their arrival, the German Army was largely a spent force, incapable of replacing their losses after the failure of their Spring Offensives.
The German Spring Offensive, while initially devastating in regards to the amount of ground taken by the Germans, lacked an overall objective and ran out of steam as advancing infantry outran both their artillery and supply lines (not to mention the amount of looting and drunkenness that occurred as the Germans overran Allied supply dumps). While the Americans were involved in countering the offensive, the majority of the fighting was conducted by the British and French with the Americans (newly arrived and as yet untested in battle) filled gaps in the line left by redeployed French units.
The Americans were involved in blunting the German attack in the Marne but it has to be said that the French knew about the attack through observation and captured German troops. While the Germans had some successes, the French, with some American support, quite thoroughly stopped the attack in its tracks before launching their own massive offensive with the support of the Americans. The Americans had an outstanding success at Saint-Mihiel where they thoroughly crushed the German-occupied salient, though again it should be noted that the Germans were in the process of withdrawing from the salient in order to shorten their line and were caught by surprise. That, however, in no way diminishes the American success but perhaps does not best reflect the American fighting ability.
A better demonstration is the Meuse-Argonne Offensive which saw a staggering 1.2 million American and French soldiers advance on German lines. This attack was of great significance in the final days of the war but was not the metaphorical straw that broke the German Empire’s back. Furthermore, the novice status of the American Expeditionary Force was fully displayed during the battle as outdated tactics and the inexperience of the units deployed led to high American casualties. At the same time, further north, the Australia Corps was going into action alongside two American divisions at the St Quentin Canal. The canal formed part of the Hindenburg Line, the last major German defends network on the Western Front and the major objective of the Allies. The Hindenburg Line was breached at the Battle of Bellicourt Tunnel by the Australians and the Americans with major support from British units. This achievement, more than any other, cemented the Allied dominance on the Western strong and signaled the inevitable defeat that forced Germany to sign the armistice.
I hope that answers your questions. If you want clarification on anything, just ask