The United States decided to enter the war on the side of the Allied powers in 1917 as a consequence of which of the following concerns:
- The sinking of the Lusitania by a German submarine in May 1915, which resulted in the deaths of 128 Americans.
- The publication in January 1917 of the Zimmerman Telegram, which proposed a military alliance between Mexico and Germany in the event the US entered the war against Germany. In exchange, Mexico was promised Texas, New Mexico, and Arizona.
- The announcement in January 1917 that Germany was going to begin sinking ships without warning again, resuming its earlier policy of unrestricted submarine warfare.
- Long-standing and strong pro-British sentiments on the part of the American public, which generally saw Germany as the aggressor nation.