Question

World war one started in 1914 but the United States did not join until 1917.

Explain to reasons why the United States finally decided to join the war on the side of the allies.


Please help me I’m so stuck

Answer 1

Over time, especially after reports of atrocities in Belgium in 1914and following the sinking of the passenger liner RMS Lusitania in 1915, the American citizens increasingly came to see Germany as the aggressor in Europe. ... On December 7, 1917, the U.S. declaredwar on Austria-Hungary.

Answer 2

The two reasons:  

• Britain intercepted the Zimmerman Telegram
• Germany resumed unrestricted submarine warfare

Context/detail:

Public outrage in the US against the Germans swept the nation following the sinking of the British ocean liner, Lusitania -- but that happened before 1917.  When a German U-boat (submarine) sank the Lusitania in May, 1915, over 1,000 persons were killed, including more than 100 Americans. The passenger liner was targeted by the Germans because they suspected weapons were being shipped to Britain in the cargo hold of the ship.

Germany managed to stave off American entry into the war at the time by pledging to stop submarine attacks.  But a couple years later the Germans  resumed unrestricted submarine warfare, and there was also an intercepted telegram (the "Zimmerman Telegram") that showed Germany was trying to secure Mexico as an ally against the United States.  

In 1917, the US declared war on Germany in response.