From 1903 to 1968, Panama was a constitutional democracy dominated by a commercially oriented oligarchy. During the 1950s, the Panamanian military began to challenge the oligarchy's political hegemony. The early 1960s saw also the beginning of sustained pressure in Panama for the renegotiation of the Hay–Bunau-Varilla Treaty, including riots that broke out in early 1964, resulting in widespread looting and dozens of deaths, and the evacuation of the American embassy.