Soviet Union
The Soviet Union officially the Union of Soviet Socialist Republics (USSR; ; sɐˈjus sɐˈvʲetskʲɪx sətsɨəlʲɪˈstʲitɕɪskʲɪx rʲɪsˈpublʲɪk; abbreviated СССР, SSSR), was a constitutionally
Constitution of the Soviet Union
There were three versions of the constitution of the Soviet Union, modeled after the 1918 Constitution established by the Russian Socialist Federative Soviet Republic , the immediate predecessor of the Union of Soviet Socialist Republics....

 socialist state
Socialist state
A socialist state generally refers to any state constitutionally dedicated to the construction of a socialist society. It is closely related to the political strategy of "state socialism", a set of ideologies and policies that believe a socialist economy can be established through government...

 that existed in Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

 between 1922 and 1991.

The Soviet Union was a single party state ruled by the Communist Party
Communist Party of the Soviet Union
The Communist Party of the Soviet Union was the only legal, ruling political party in the Soviet Union and one of the largest communist organizations in the world...

 from its foundation until 1990. Even though the USSR was technically a union
Political union
A political union is a type of state which is composed of or created out of smaller states. Unlike a personal union, the individual states share a common government and the union is recognized internationally as a single political entity...

 of 15 independent Soviet republics
Republics of the Soviet Union
The Republics of the Soviet Union or the Union Republics of the Soviet Union were ethnically-based administrative units that were subordinated directly to the Government of the Soviet Union...

, its government
Politics of the Soviet Union
The political system of the Soviet Union was characterized by the superior role of the Communist Party of the Soviet Union , the only party permitted by Constitution.For information about the government, see Government of the Soviet Union-Background:...

 and economy
Economy of the Soviet Union
The economy of the Union of Soviet Socialist Republics was based on a system of state ownership of the means of production, collective farming, industrial manufacturing and centralized administrative planning...

 was highly centralized.

The Russian Revolution of 1917
Russian Revolution of 1917
The Russian Revolution is the collective term for a series of revolutions in Russia in 1917, which destroyed the Tsarist autocracy and led to the creation of the Soviet Union. The Tsar was deposed and replaced by a provisional government in the first revolution of February 1917...

 caused the downfall of the Russian Empire
Russian Empire
The Russian Empire was a state that existed from 1721 until the Russian Revolution of 1917. It was the successor to the Tsardom of Russia and the predecessor of the Soviet Union...


1895    In Saint Petersburg, Russian scientist Alexander Stepanovich Popov demonstrates to the Russian Physical and Chemical Society his invention, the Popov lightning detector — a primitive radio receiver. In some parts of the former Soviet Union the anniversary of this day is celebrated as Radio Day.

1917    Cheka, the first Soviet secret police, is founded.

1918    The Soviet Union adopts the Gregorian calendar (on 1 February according to the Julian calendar).

1920    Azerbaijan is added to the Soviet Union.

1920    Part of Petsamo Province is ceded by the Soviet Union to Finland.

1921    The second Peace of Riga between Poland and Soviet Union.

1922    The Treaty of Rapallo, pursuant to which Germany and the Soviet Union re-establish diplomatic relations, is signed.

1922    The Union of Soviet Socialist Republics is formed.

1924    The United Kingdom recognizes the USSR.

1924    The Soviet Union signs an agreement with the Peking government, referring to Outer Mongolia as an "integral part of the Republic of China", whose "sovereignty" therein the Soviet Union promises to respect.