there were four countries that had control of a region of germany.russia zone was in the east part of germany,the british had control of the northern region,the united states had control of the southern region of germany,and the french had conrtol of a region in the east along there border with germany.
This question implies that the countries had a choice. Some were attacked and had to surrender. Germany was such a threat to world peace before the war started, that Britain and France met and allowed Germany to take over control of some border land and countries. Mainly, the small countries could not resist the German Army. Some wanted to remain neutral but Germany had to attack them to get to France and England.
World War I ended with uprisings and revolutions in several European countries. Communists took advantage of these uprisings and tried to take control of those countries. They were successful in Russia, and also tried in Germany (where they did control parts like Bavaria briefly) and Hungary (where they took control for about five months).