On 6th April 1917, America declared a war against Germany.

1)       Even though America was not directly involved in the war against Germany, it condemned Germany aggression and issued several warnings to Germany.
2)       But Germany refused to pay heed to American warnings and continued using submarines indiscriminately.
3)       German submarines targeted a boat named Lusitania and wrecked (broken) it.
4)       Several American passengers on board were killed.

5)       Therefore, at last America waged a war against Germany on 6th April 1917.