The United States eventually joined the Allied powers during World War I. The US did not join the Allied powers until 1917, 3 years after World War I started in Europe. The US joined the Allied powers because of the actions taken by the German government/military against the US. The Germans, who were part of the Central powers, tried to convince the Mexican military to invade the US as a means to distract them from World War I. However, the message relaying this idea was intercepted by the Allied powers. Shortly after the US found out about this, they entered World War I.