That "lesson" doesn't make sense to me. Republics do sometimes devolve into totalitarianism or are crushed by totalitarian nations, but dictatorships are also crushed by Republics, and often collapse under their own weight. This is just because all government systems fall eventually, either evolving, devolving, or being crushed by something else. There's no reason to single out Republics as somehow unique in their history of failure.
(And really, what is the "lesson" we're supposed to learn, exactly? That no one should ever try to have a representative democracy? Oppressive tyrants are where it's at?)