It's pretty clear in the original Star Wars that the Rebels have a single base, the destruction of which would crush the rebellion. If we don't want to accept the Star Wars universe as movie-simplistic, we are free to deal with some EU stuff ... which is good and fine, but I can't comment on it.
But the one-base idea presented in Star Wars implies in the sequel that Echo Base on Hoth is also a singular and unique rebel location ... likely so, just as planets in the Star Wars universe consist entirely of single ecological environments.
It's ridiculously simplistic, but it's Star Wars.
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