I believe the correct answer is: because Belgium didn’t
agree upon Germany’s request to allow a free escort through their country to
invade France.
During the First
World War, Netherlands and Belgium both announced that they will sustain the
neutrality, but Belgium was invaded in August 1914. Invasion of Belgium was a
military campaign, approved by the German Emperor, Kaiser Wilhelm II, as
Belgium didn’t allow a free escort throughout their country to let Germany
invade France.
The plan also included the option to go through Netherlands,
but Kaiser decided otherwise.
