Why did Germany march through Belgium?

The Belgian government mobilised its armed forces on 31 July and a state of heightened alert (Kriegsgefahr) was proclaimed in Germany. On 2 August, the German government sent an ultimatum to Belgium, demanding passage through the country and German forces invaded Luxembourg.

To attack the french

Explanation:

The Germans were getting their troops in place to attack but Belgium wouldn't let them through and so they forced their way through which outraged the world because they violated a treaty they had with London by doing it and it led to Europe taking action on them.