What event happened in april of 1917 that changed the direction of world war i

The United States declared war on Germany.  

Explanation:

After the rupture of diplomatic relations with Germany on Feb. 3, 1917, events pushed the United States inexorably along the road to war.  

The war resolution was approved by the Senate on April 3, and by the House of Representatives on April 6. The presidential declaration of war followed immediately.

The entry of the United States was the turning point of the war, because it made the eventual defeat of Germany possible.

the american revolution was by the middle and upper class, and the french was by the lower and middle class.