COLLEGE STATION, Texas — With the fall of the Berlin Wall in 1989 and the relatively nonviolent overthrow of communism throughout Central and Eastern Europe, optimists predicted a new golden age of a world filled with peaceful democracies. History, for some, seemed to have come to an end. But the optimists have proved to be misguided, as the world's powers, great and small, drew their own, often conflicting, lessons from the past.