The US had a policy of isolationism.

Even as the sold weapons, the US remained neutral.

The Lusitania was sunk, killing 128 Americans.

The Zimmermann note tried to get Mexico to fight America.

America finally joined the war, siding with the Triple Entente.

Propaganda urged Americans to help those in the war.

American solider fought terrible Trench Warfare.

The League of Nations was created, but the US didn't join.