Lazy sci-fi. Every civilization except humans is unified and monolithic, or has at most maybe 2 subgroups, because it’s hard to invent thousands of years of his

Lazy sci-fi. Every civilization except humans is unified and monolithic, or has at most maybe 2 subgroups, because it’s hard to invent thousands of years of history. And not just fiction, but science also: “Why haven’t aliens done X by now?”