Which of the following political philosophers wrote that the ends justify the means so it was often necessary for rulers to use any means available to maintain power?

Niccolo Machiavelli

Explanation:

That was one of his main principals, and what he was most famous for saying/writing.

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