 Complete the following phrase:  Although committed to preserving the Soviet state and to its socialist ideals, Gorbachev believed significant reform was necessary, particularly after the 1986 Chernobyl disaster. He withdrew from the SovietAfghan War and embarked on summits with United States president Ronald Reagan to limit nuclear weapons and end the Cold War. Domestically, his policy of glasnost openness allowed for enhanced freedom of speech and press, while his perestroika restructuring sought to decentralize economic decision making to improve efficiency. His democratization measures and formation of the elected Congress of Peoples Deputies undermined the one-party state. Gorbachev declined to intervene militarily when various Eastern Bloc countries abandoned MarxistLeninist goverce in 198990. Internally, growing nationalist sentiment threatened to break up the Soviet Union, leading MarxistLeninist hardliners to launch the unsuccessful 