The Union of Soviet Socialist Republics, also known as the Soviet Union or the USSR, was a vast Eurasian country that existed from 1922 to 1991. At its peak, the USSR was by far the world's largest country, encompassing all of Northern Asia and most of Eastern Europe and stretching more than 10,900 kilometers (6,800 miles) from end to end and roughly 4,500 km (2,800 mi) top to bottom. The USSR touched 11 of the world's 24 time zones and had a land area of more than 22,402,200 km² (8,649,500 mi²), nearly matching that of the entire continent of North America. In the late 1980s, the Soviet population reached more than 288 million, making it the third-most populous nation in the world.
The USSR was an undisputed superpower during most of its existence, a communist counterpart to the democratic and capitalistic United States, with a command economy built around the concepts of collectivization and industrialization. However, social and political unrest, particularly between the country's constituent states and its central government, would eventually lead to its dissolution. From 1988 to 1991, the USSR gradually broke apart into 25 smaller territories, which coalesced into the 15 post-Soviet republics (and a few still-unrecognized territories) known today. The USSR was officially dissolved in December 1992. The largest of the resulting territories, the Russian Federation, assumed its place in the United Nations and other international organizations.
While the current roster of 15 former Soviet republics has held steady for more than three decades, Russia has shown a marked interest in regaining the USSR's former territory. In February 2022, Russian forces invaded Ukraine in a move that was immediately condemned by nearly every other nation in the world (with China and Belarus being notable exceptions). Nor was this the first event of its kind. At various times from 1994 to 2009, Russia deployed troops to its own region of Chechnya to keep the territory from seceding; and in 2014, Russia invaded and annexed Ukraine's Crimean peninsula.
The USSR was one of the many countries involved in World War II, though it played a complicated role in the conflict. In 1939, the country signed a non-aggression pact with Nazi Germany and participated in Germany's takeover of Poland. However, German leader Adolf Hitler turned on the Soviets and invaded in June of 1941, violating the non-aggression pact. This led to the Soviets switching sides and joining the Allied forces. Despite suffering arguably the most casualties of any nation in WWII, Russia stayed in the fight and the Allies eventually defeated Germany, Japan, and the other Axis powers.
With WWII over, the USSR founded the Eastern Bloc and launched what came to be known as the Cold War, an undeclared arms race against capitalist nations, NATO, and especially the United States. The stockpiling of nuclear weapons per country was a particular point of emphasis.
Fifteen countries existing today were once part of the former USSR: Armenia, Georgia, Lithuania, Turkmenistan, Azerbaijan, Kazakhstan, Moldova, Belarus, Ukraine, Kyrgyzstan, Russia, Estonia, Latvia, Tajikistan, and Uzbekistan.