Complex sentence: For centuries, Georgia's ability to ward off invaders was due largely to its culture of encouraging martial arts; it endured in times when other populous countries, both small and large, vanished without a trace.
Split into simpler sentences: For centuries, Georgia's ability to ward off invaders was due largely to its culture of encouraging martial arts. Georgia was able to endure whole eras in which other numerous countries, both small and large, vanished without a trace.