Created from the Russian empire in the aftermath of the 1917 Russian Revolution, the Soviet Union was the largest country in the world. It comprised fifteen republics: Russia, Belarus, Ukraine, Georgia, Armenia, Moldova, Azerbaijan, Kazakhstan, Kyrgyzstan, Turkmenistan, Tajikistan, Uzbekistan, and the three Baltic states Estonia, Latvia, and Lithuania (annexed in 1940). After the Second World War, the Soviet Union emerged as a superpower in rivalry with the US, leading to the Cold War. Decades of repression and economic failure eventually led to attempts at liberalization and economic reform under President Mikhail Gorbachev during the 1980s. The Soviet Union was formally dissolved in 1991, some of its constituents joining a looser confederation, the Commonwealth of Independent States