Answer:
Russia abandoning the Triple Entente due to the Russian Revolution and Germany attacking American ships.
Explanation:
In 1914, the outbreak of World War I determined the consumption of a tension that had developed between the nations of Europe since the nineteenth century. Before the war, the United States advocated open-door policy as the best solution to strong imperialist competition. In this regard, US government officials believed that all imperialists had equal rights to exploit Afro-Asian territories.
Despite this conciliatory premise, European countries preferred war as a solution. In this new context, the United States began to profit at the expense of World War I. In a short time, European nations needed huge amounts of food and weapons for the conflict. Although remaining neutral for reasons of interest and affinity, the US government exported its products only to the members of the Triple Entente.
US supportive behavior soon deepened, especially as we looked at the lending of funds for war in Europe. Until that time, the conflict had turned into a very lucrative and beneficial event for the US economy. At the political level, the United States hoped that the nation could be further strengthened by possibly assuming the status of peace treaty broker.
Such projections would change course in the year 1917. That year the Russians abandoned the Triple Entente with the development of the Russian Revolution. For the central powers this would be the ideal opportunity to win the conflict. Not coincidentally, the Germans set in motion a bold plan to attack vessels supplying England with supplies and weapons. In this context, US ships were targeted by German submarines.
At that time American neutrality became unsustainable for two fundamental reasons. First, because the loss of the vessels was a clear provocation that required a more incisive response from the US government. In addition, the departure of the Russians increased the risk of the Triple Entente being defeated and, consequently, of the US bankers not receiving the huge amounts of money lent to the warring countries.
On April 6, 1917, the United States declared war on the Germans and their allies. A large volume of soldiers, tanks, ships and warplanes were used to ensure the Entente's victory. Before long, the German and Austrian troops were defeated. In November 1918, Compiègne's armistice arranged for the Germans to withdraw and the Triple Entente to quickly win.