Germany split for a few reasons. One reason is that the western side of Germany was controlled and ran by the United States, French, and British forces. Right when it became available, the plan was to become an independent country.
Right when this happened, the western and eastern parts of Germany split and became separate countries; East and West Germany. West Germany became an independent, democratic nation, controlled by the Allied forces. East Germany, controlled by the Soviets, was never actually allowed to form an independent or democratic government.
East and West Germany we never allowed to associate with each other. The Berlin Wall stopped them East Germans fleeing into West Germany in search of freedom and independence.