In World War 1 why did Germany invade neutral Belgium?

Invasion of Belgium in 1914The frontier between Germany and France was well fortified on both sides at the time, and a direct attack would probably not have succeeded.

By 1905 the German General Staff, the central planning agency of the German army, had worked out in great detail a plan for attacking France along its long and exposed northern border despite the fact that this involved violating Belgian neutrality. The main plan was called the Schlieffen-Plan. One of the problems was that the General Staff was made up of technocrats who had very little idea of the 'big picture'. They didn't have much of a grasp of international relations.

When Moltle, Junior took over as Head of the General Staff in 1906, he made a several modifications to the plan. He was convinced that Germany could knock France out of the war in six weeks - but the plan didn't work. All the main assumptions were just so many miscalculations. For example, it was assumed that Belgium wouldn't fight and that Britain would stay out of the war ...