How did the german invasion of Belgium happen?
Germany has invaded Belgium on two occasions, the first in WWI and the second in WWII. The first invasion arose when German forces sent Belgium an ultimatum which demanded that Belgian forces surrendered to Germany in order for German forces to open up a new front against France. The Belgian government refused and Germany declared war in response.
The Second invasion occurred under similar circumstances, where Germany demanded Belgium to surrender in order for the German army to be able to attack France and expand their empire. In this case Belgium was again invaded and taken by German forces. Belgium would remain under German control until 1944 when it was liberated by Allied troops.