The first event was the sinking of merchant ships by Germany's U-boats.
The second event was Germany's letter to Mexico, asking Mexico to attack US in return for Texas, New Mexico, and Arizona back.The final event would be the bombing of Pearl Harbor by the Japanese.
The first two events caused US to join the allies in WW2.
The third event caused US to declare war on Japan. And because Japan had alliances with Germany, US got involved in WW2.