在1941年苏德战争爆发之前，苏联就已经竭尽全力向西扩张，在1939年到1940年期间苏联接连吞并西部邻国的土地，将边境线向西推进了400–500公里，占领了46万平方公里的土地，人口2200万，苏联从二战时期就有了乱划缓冲区的习惯，而且很明显，一直到现在俄罗斯都在保留这个习惯，并不惜发动一场战争。
苏德互不侵犯条约
During 1937 and 1938, the Soviet Union repeatedly hoped to unite Britain and France to encircle Germany, which was expanding outward, but Britain and France scoffed at the idea of forming a common defense alliance with the Soviet Union, and instead continued to appease Germany more vigorously until Germany completely annexed the Czech Republic in 1939, and the Soviet Union completely lost hope in Britain and France, and turned around and signed the "Soviet-German Non-Aggression Pact" with Germany in the summer of 1939.
Although it was ostensibly a non-aggression pact, it also had a secret clause in the partition of Poland, and at the same time the Soviet Union and Germany divided their spheres of influence in Europe, and the Soviet Union gained Finland, the three Baltic states, and Romanian Bessarabia. Stalin's attempt to annex his little brother in the West was simply to expand his borders as far west as possible to make room for possible wars to follow.
According to the Soviet Union's concept, with the rise of Germany, the relationship between the Soviet Union and Germany is undergoing very subtle changes, and Stalin is very keenly aware that there will definitely be a big war between the Soviet Union and Germany in the future, so according to the Soviet high-level assumptions, if there is a war with Germany in the future, the battlefield will inevitably be limited to the newly expanded territory. These territories are known as buffer zones, as is the case in Russia today.
苏联吞并的领土
After the First World War, Poland, which had been destroyed for more than 100 years, was successfully restored, and because of the defeat of Tsarist Russia in the later stage of World War I, losing Western Ukraine and Western Belarus and other regions, Britain and France naturally did not mind being generous to others, and generously divided these regions into Poland. In the Soviet-German non-aggression pact, the Soviet Union and Germany were bounded by the Narev River and the Vistula River, and as a result, Poland perished more than a month after the German invasion.
After the Soviet Union annexed eastern Poland, the car of outward expansion immediately could not be stopped, the Soviet Union soon looked at the next target in the northwest of Finland, Finland was also independent after World War I, because Finland's Karelia was too close to the important city of Leningrad of the Soviet Union, so the Soviet Union wanted to exchange territory with Finland, but Finland refused, and then the Soviet Union casually found a reason to start a war against Finland, and then after four months of fighting, more than 300,000 casualties before taking the Karelian region.
In 1940, the Soviet Union began to penetrate into the three Baltic states, and countries such as Estonia, Lithuania and Latvia owned 174,000 square kilometers of land, which were once part of the Russian Empire, but remained independent after World War I. Thus, in June 1940, the Soviet army of 300,000 troops marched into the three Baltic states, after which the three Baltic states were forced to join the Soviet Union through a referendum. (Referendum by the bayonets of the Soviet army).
The last territories of Soviet expansion were Bessarabia in Romania and Bukovina in the north. The Soviet-German Non-Aggression Pact stipulated the rights and interests of the Soviet Union in Bessarabia, and as a result, in June 1940, the Soviet Union frightened Romania, and the Romanian king obediently withdrew from Bessarabia and was forced to cede Bessarabia to the Soviet Union.