 His democratization measures and formation of the elected Congress of People's Deputies undermined the one-party state.Gorbachev declined to intervene militarily when various Eastern Bloc countries abandoned Marxist-Leninist governance in 1989–90.Internally, growing nationalist sentiment threatened to break up the Soviet Union, leading Marxist-Leninist hardliners to launch the unsuccessful August Coup against Gorbachev in 1991.