What was the fight about in the Vietnam War

It was a proxy war. The U.S was getting worried about the spread of communism. The Vietnam War was just the U.S trying to prevent the spread of communism reaching the south of Vietnam which wasn't communist

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