it was started in the 1930's.. aka, it was around back then. if you really want to learn a lot about the rasta movement, bob's book "catch a fire" has a shitload to do with the rasta culture long before they even get into his life. check it out if you're interested.
buffalo soldier was a reference black soldiers fighting indians. It says so right in the little CD pamphlet I have in my hands right now. Buffalo soldiers were indians.