MOSCOW (AP) – Before Mikhail Gorbachev, the Soviet Union seemed an immovable superpower in perpetual antagonism to the United States. But with a breathtaking series of reforms, Gorbachev changed all that – and redirected the course of the 20th century. He died Tuesday at a Moscow hospital at age 91. Alongside Ronald Reagan and Margaret Thatcher, he was a key protagonist in a global drama. Under Gorbachev, the Berlin Wall crumbled, thousands of political prisoners were released and millions of people who had known only communism got their first real taste of freedom. But Gorbachev was unable to control the forces he unleashed. He ultimately waged a losing battle to salvage a crumbling empire.