Why did Americans agree to
participate in the UN after World War II when
many had rejected participation in the League of
Nations after World War I?

This was because of a multitude of factors, but primarily due to The Bombing of Pearl Harbor.

Explanation:

During the end of the 1930's and early 1940's we had the Neutrality Act, which basically said no interfering with other's wars. We still sold good to both the Axis and Allies, but they had to pay immediately and had no pick it up, no credit, no shipping. Japan was allied with the Axis during 1941, Japan decided to bomb Pearl Harbor. This was an attack on American Soil, our patriotism basically went into effect and since we were sided with the allies, we decided to join them in the European Front.

i'd assume india mainly because of how isolated japan was.   plus it is a whole china away.

martin luther king (1929-1968) was an activist for the african american rights, mr. king has a profile of a kind leader that built a tenacity, respect and full of hope future. he was an activist through civil disobedience and no violence pressure mechanisms. he tried to build a more egalitarian and fair society. his efforts carried a reivindication message of the civilian rights to every west corners. for that reason, he won the nobel prize in 1964.