Marx held a very linear view of progression of historical stages, and as was quite common at the time, some regions were considered more advanced along that progression while some where more backwards. In short, a progression is: primitive communism -> slavery -> feudalism -> bourgeois capitalism -> socialism -> communism (later two being in the future for Marx). "Asiatic despotism" branches of somewhere early of, maybe from slavery, and is somewhat of a dead end, until nudged back on track by outside interference.

So, "uncivilized" would be in either of the pre-capitalist stages. I'm not sure to what work by Marx I would point you to, but reading The origin of family, private property and the state by Engels would mostly answer your questions.