Civilization might spread in D.C if there's enough water to go around. True, raiders will be raiders and steal from every other caravan, but if the brotherhood gets more recruits than raiders won't be too much of a problem, clean water spreads, and people can focus a little less on survival and a little more on reconstruction, and people will form settlements in these reconsturcted areas, and since bos controls the water, elder lyons might be recognized as leader of dc. He signs some bills on the destruction of raiders, feral ghouls, super mutants, enclave remnants, etc. and there you go, civilized D.C.