Russia during the interwar period saw the rise of the Soviet Union as the Bolsheviks consolidated their regime. Equally, it saw the emergence of Stalin during the 1920s as Lenin's successor. Overall, the USSR's military and industry expanded considerably during the period.
At the beginning of the 1920s the Russian Civil War followed World War One. This lasted into the early '20s as the Red Army defeated the various opposition armies in Russia. The Whites lacked a solid coalition and gradually their armies disbanded. Trotsky inspired the newly formed Red Army to victory, and the Bolsheviks access to railroads gave their armies a crucial advantage.
In 1922, the Bolsheviks established the USSR. This union included republics such as Ukraine and Belarus. Bolshevik Party leader Lenin became the first Soviet Premier of the USSR.
After World War One the Russian economy needed reviving. The failure of War Communism merely highlighted the Bolsheviks needed to pursue an alternative economic policy. Lenin advocated the New Economic Policy, which was otherwise called NEP, as a means of providing a platform for economic recovery.
Lenin considered NEP as state capitalism, and was really more of a mixed economy. It introduced a degree of free market reforms in the USSR. As such, NEP did not fit easily with the Bolshevik's ideology. However, the Bolsheviks still approved of the policy; and the Soviet economy did begin to recover. Agricultural output increased considerably with grain surpluses, while Russian rail-roads also expanded.
The communist revolution did not spread to other countries as Lenin and his party had anticipated. The party established Communist International to support other left-wing parties in Europe. In Germany there was an attempted communist coup, which was subsequently disbanded. Communist parties gained in increasing amount of support in Italy, but they could not establish communism there either.
Consequently, the Soviet Union entered into diplomatic agreements with Germany. The Treaty of Rapallo in 1922 brought the USSR and Germany closer, allowing for potential trade and even secret German re-armament in Russia.
By the mid 1920s Lenin passed, which left leadership of the Bolshevik Party open to a potential successor. Who that would be was something of a mystery, although Stalin and Trotsky were two potential candidates. It was Stalin, thanks to his positions within the Politburo, that was able to emerge as Soviet Premier by 1927. Upon his emergence opposition such as Trotsky left the country, and the OGPU disbanded other groups.
Stalin's emergence marked the new era for the Soviet Union. Whether a golden era or not, his economic policies did expand the USSR's heavy industry. This was largely due to the Five Year Plans that Stalin introduced as an alternative to NEP. The plans laid down a number of targets that aimed to close the gap on Western industry.
Overall, the Five Year Plans did increase Soviet industrial productivity markedly. The number of Russian industrial workers more than doubled to 12.6 million. Although the policy of Collectivization was a step backwards for the agriculture and even resulted in famines during the early 1930s.
Other Five Year Plans in the 1930s had brought further industrial expansion, particularly in industries such as steel. As such, by 1937 the Five Year Plans had ensured that Russian heavy industry was much more competitive. This was just as well as the Treaty of Versailles was gradually overturned by Nazi Germany, and the potential for war in Europe was becoming closer.
The Nationalists established another fascist regime in Spain. There a Civil War emerged between the Nationalists and left-wing Republicans. Stalin and the USSR provided military supplies for the Republican armies, but that was not enough to ensure a victory. With Germany and Italy throwing their support behind the Nationalists, it was they that won that war.
The Soviet Union had not made any diplomatic agreements with Western Europe. Britain and France remained weary of the USSR, and in 1938 the Munich conference did not involve any input from Stalin. Instead, Germany falsely agreed to a number of diplomatic concessions in Eastern Europe, most notably in relation to Czechoslovakia. The subsequent German occupation of Czechoslovakia was the first step to war.
Stalin entered into diplomacy with the Nazis. This resulted in the Nazi-Soviet Pact in 1939 whereby the Soviet Union consented to a German invasion of Poland and promised neutrality. So the USSR did not join the West's side after the German invasion of Poland.
Therefore, by the end of the decade the USSR had agreed to an unlikely pact with Germany. Soviet and German propaganda glossed over some confusion on both sides. At any rate, the USSR continued to expand the Red Army, which was soon mobilized against Finland in 1939. In 1941, the German army invaded the USSR and the war in the East began.