The 1940s were one of the most turbulent decades of modern European history, beginning with an all-out war and ending divided between two firmly established blocs. Nazi Germany and the allied campaign to stop Adolf Hitler's expansionism defined the first half of the 1940s, in what we know today as the Second World War. After 1945 and Germany's surrender, Europe became a theater of political antagonism between the superpowers of the East and West: the Soviet Union and the United States.
Beginning of the Decade
The year 1940 found Europe divided, but in two opposing military blocs: the allied forces, including the United Kingdom and France and the Axis forces, comprising Germany and Italy, while the rest of Europe's countries allied with one or the other side as conflicts went on. The major political concepts leading to the war was Adolf Hitler's willingness to avenge for the humiliating treaty which ended the Great War (World War I) , as well as Nazi ideology concerning the German nation's ethnic superiority and "lebensraum," which in German means living space (for "Aryans" to expand). Allied forces banded together to prevent the expansion of Germany's and Italy's fascist totalitarian model.
End of the Decade --- West
After a successful western European campaign, which included the liberation of France, the Netherlands, Belgium and Norway among others, western European countries remained loyal to parliamentary democratic politics. With the aim of protecting free-market capitalism and defending themselves against the so-called Eastern Bloc, western European countries allied with the United States to form the North Atlantic Treaty Organization (NATO) in 1949. The Marshall Plan was another incentive for governments and the public in western Europe to adopt a strong pro-U.S. stance.
The Soviets counterattacked from the East, liberating a series of countries from Nazi occupation. At the end of the war, in 1945, these liberated countries came under the influence of the Soviet Union to form what was known in the West as the "Eastern Bloc." Eastern European countries (Bulgaria, Romania, Hungary, Poland, Czechoslovakia, East Germany) were forced to adopt the economic system of socialism (state ownership of means of production), while following the political position dictated by the Soviet Union. These countries remained independent, but the Baltic States (Estonia, Latvia, Lithuania) were incorporated in the Soviet Union.
Beginning of Alliances
As a measure to prevent another mass-scale conflict, European nations started forging political and economic alliances in the late 1940s. The Treaty of Dunkirk between France and Britain in 1947, as well as the Brussels Treaty the following year, between Britain, France, Belgium, Luxembourg and the Netherlands solidified the alliance between western European nations. Political integration in eastern Europe was slower, with the Warsaw Pact (East's NATO equivalent) being established in 1955.