 Major trends in Oklahoma history after the Depression era included the rise again of tribal sovereignty (including the issuance of tribal automobile license plates, and the opening of tribal smoke shops, casinos, grocery stores, and other commercial enterprises), the rapid growth of suburban Oklahoma City and Tulsa, the drop in population in Western Oklahoma, the oil boom of the 1980s and the oil bust of the 1990s.In recent years, major efforts have been made by state and local leaders to revive Oklahoma's small towns and population centers, which had seen major decline following the oil bust.But Oklahoma City and Tulsa remain economically active in their effort to diversify as the state focuses more into medical research, health, finance, and manufacturing.