Colonization can change a culture. When you conquer, you force new language, new laws, and new rules. By threat of violence, people must assimilate or die. But because violence is expensive, it's more likely that the "assimilate or die phenomena" happens through the marketplace. You must adapt to the conqueror's commerce or die.

When you conquer or decimate a population, you force the majority to assimilate, but the rest turn into a subculture. The remaining Inuits and Native Americans who have preserved their norms are evidence of cultural resistance. They're small, but they've preserved their system. If you enter their enclaves, you must obey their rules. And the rules are self-re-enforcing. By obeying the rules, you then perpetuate them to newcomers. Outside of an external force, cultures drift in hundred-year scales. Or they branch off through geographic isolation, like the Americans, or the North and South Koreas, and then their isolated subcultures flourish, like on the Galapagos Islands. The timescales themselves in a way bolster Dawkins theory of memes, in that memes are at least relatively as resilient to the comings and goings of their hosts as genes.

Counterpoint regarding the removal of power structures

After World War II, a U.S. general was once asked something along the lines of, "What do you say about how you're just driving the Nazis underground?" He then supposedly replied, "Yes, we're driving them underground. Six feet underground." The Nazi affiliation network was dismantled and destroyed, but the German people and their culture were not.