What happened in the ww1

World War II was the biggest and deadliest war in history, involving more than 30 countries. Sparked by the 1939 Nazi invasion of Poland, the war dragged on for six bloody years until the Allies defeated Nazi Germany and Japan in 1945.

Explanation:

although world war i began in 1914, the united states did not join the war until 1917. the additional firepower, resources, and soldiers of the u.s. to tip the balance of the war in favor of the allies. remaining neutral. when war broke out in 1914, the united states had a policy of neutrality.