Tens of thousands of Chileans marched through Santiago on Sunday to commemorate 40 years ago when Chilean air force jets bombed the palace, helping to overthrow an elected socialist government and obliterate what had been one of South America’s healthiest democracies.The resulting military dictatorship of Gen. Augusto Pinochet, who ruled for 17 years, suspended political and civil rights; censored the press; and imprisoned, tortured, exiled, abducted or killed tens of thousands of its opponents.