that existed in Eurasia
between 1922 and 1991.
The Soviet Union was a single party state ruled by the Communist Party
from its foundation until 1990. Even though the USSR was technically a union
of 15 independent Soviet republics
, its government
was highly centralized.
The Russian Revolution of 1917
caused the downfall of the Russian Empire
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.