What event provoked the U. S. to join the military combat in WWII and what did Hitler do that caused the war?

The U.S joined the military combat in WWII after the attack on pearl harbor.

On 7 December 1941, while German armies were freezing before Moscow, Japan suddenly pushed the United States into the struggle by attacking the American naval base at Pearl Harbor, Hawaii. Four days later Hitler declared war on the United States.

And what did hitler do to cause the war?

Hitler smashed the nation's democratic institutions and transformed Germany into a war state intent on conquering Europe for the benefit of the so-called Aryan race. His invasion of Poland on September 1, 1939, triggered the European phase of World War II

Explanation:

World War 2 started on 3 September 1939. Although there were many causes for the war, like the failure of the Treaty of Versailles, the threat of communism, and appeasement. Hitler and the Nazi party were the main cause, they were linked with all other causes, making them stand out as the ‘main cause’. Everything that had happened after World War 1; the Treaty of Versailles, the Great Depression, Communism, and Fascism, all helped Hitler gain trust from the Germans, as he said he would ‘make Germany great again’.

Explanation:

the answer to your question is a. the salt plains

in 1811, he led an expedition, known as the george c. sibley expedition, to improve relations with the pawnee and kansa tribes, and also to locate the rumored jefferson's salt mountain

to demand women’s suffrage