Why? Settling new places doesn’t have to mean expanding the existing polity: the settlements can be self-governing. See the Polynesian expansion through the Pac

Why? Settling new places doesn’t have to mean expanding the existing polity: the settlements can be self-governing. See the Polynesian expansion through the Pacific, which to me is a closer (and more hopeful) analogy to space colonization than anything nineteenth-century Europeans or ancient empires did. And so long as we’re just thinking of this solar system, there’s also the question of whether what’s important is transit time or communication time. Historically those were identical; now very much not.