North America 1917: United States Enters the Great War

While the US was embroiled in Latin America, the Great War had erupted across Europe, pitting the German-led Central Powers against France, Britain and Russia and their allies. At first the US was neutral, but gradually it came to see Germany as the greater threat. Germany's 1917 announcement of unrestricted submarine warfare in an attempt to starve Britain into surrender further aggravated its relations with the US and, when German plans to incite a war between Mexico and the US were uncovered, America declared war.

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16 May 1916 US occupation of the Dominican Republic ▲

The United States intervened in the Dominican Republic to overthrow recent coup-leader Desiderio Arias and maintain order. in wikipedia

4 Aug 1916–1 Apr 1917 Treaty of the Danish West Indies ▲

After a series of negotiations for the purchase of the Danish West Indies—which had begun for some islands as early as 1867—the United States signed the Treaty of the Danish West Indies with Denmark on 4 August 1916, agreeing to purchase the islands for a sum of US$25,000,000 in gold. After ratifications were exchanged on 17 January 1917, and the US presented the money on 31 March, the islands were formally transferred to the US, becoming the US Virgin Islands. in wikipedia

1 Feb 1917 Germany announces resumption of unrestricted submarine warfare ▲

Germany announces resumption of unrestricted submarine warfare in wikipedia

1 Mar 1917 Zimmermann Telegram ▲

In January 1917, German Foreign Secretary Arthur Zimmermann messaged Carranza’s government in Mexico proposing an alliance between the two countries should the United States declare war. In exchange for Mexico’s assistance against the US, Germany was prepared to recognize that country’s reclamation of most the the land lost in the 1848 Treaty of Guadalupe-Hidalgo, as well as Texas. However, the effort backfired: Mexico declined the offer, concluding that its then-fractured military could not win against the US; and the telegram’s publication decisively turned US public sentiment in favor of the Allies. in wikipedia

8–12 Mar 1917 February Revolution ▲

Mass demonstrations broke out in Petrograd, capital of the Russian Empire, in March (late February in the Julian calendar) in response to economic and social problems, compounded by the strain of World War I. After a few days, the mutinous Russian Army sided with the revolutionaries, forcing Tsar Nicholas II to abdicate in favor of a Provisional Government under Prince Georgy Lvov. in wikipedia

6 Apr 1917 US declaration of war on Germany ▲

On 2 April 1917, United States President Woodrow Wilson asked a special joint session of the US Congress to declare war on the German Empire. Congress obliged by declaring war on the 6th, with the resolution passing 82 to 6 in the Senate and 373 to 50 in the House. in wikipedia