April 1917 President Wilson asked congress to approve a declaration of War. The United States decision to enter the war had a great deal to do with the sudden change in German Military strategy. In January of 1917 the German's resumed the practice of Unrestricted Submarine Warfare. In the first weeks of March Germany sunk 5 unarmed US merchant ships. Previously in 1916, after Germany sank the Sussex a US merchant ship, the US threatened to enter the war, and Germany backed down. They promised not to sink merchant or passenger ships without warning. They kept this promise until 1917. Other immediate causes for US entering the war are the 1) Zimmerman Telegram (intercepted by British intelligence a note between Germany and Mexico proposing that the two countries align) and 2) the Russian Revolution.
sinking of lusitania
by Gerrnan submarine
by Gerrnan submarine
The atomic bombings of Hiroshima and Nagasaki.
They did not lead to war; they were part of the war. They were, however, factors in the United States' decision to enter the war.
The Sinking of the Lusitania and the Zimmerman telegram.
Japans attack on Pearl Harbor, Hawaii
Two key German actions that prompted the U.S. to enter World War I were unrestricted submarine warfare and the Zimmermann Telegram. Germany's resumption of unrestricted submarine warfare in early 1917 led to the sinking of American merchant ships, heightening tensions. Additionally, the interception of the Zimmermann Telegram, in which Germany proposed a military alliance with Mexico against the U.S., further inflamed public opinion and pushed the U.S. towards war.
That is a complex answer. You should be more specific on what you want to know. Like what led up to to the war, that caused Germany to let Hitler come to power. Or what led the United States to enter the war.
The Vietnam war
The rise of Naziism, which swept across Czechoslovakia and Poland.
None. ___ A big effect. The actions of the Nazis in Europe led to a global war, one in which Canada was involved.