Answer:
Communism, as a political movement, was spread across Europe by the workers movement during the 19th and early 20th centuries in different revolutionary waves until the one following WWI that sparked the Russian Revolution of 1917 as well as attempted revolutions in Hungary, Germany and other countries in the following years.
Communist regimes aligned with the Soviet Union that lasted until the early 90’s, spread throughout Europe after WWII, when the victorious allies divided Europe between the west (France, UK, Iceland, West Germany) - under mainly American influence - and east (Poland, Albania, Bulgaria, Croatia, Estonia, Latvia, Lithuania, East Germany.) - under Soviet influence. People on the Eastern side of Europe lived in a communist society, while the people on the western side were well taken care of by the US.
The Soviets then proceeded to put the local communist parties in charge of each country, under the tutelage of Moscow. And that’s how the “Eastern Bloc” began.
