What caused Belgium to declare itself a neutral nation three years before the outbreak of World War 2?

Belgium had been a major battlefield in WW 1 with all the devastation, loss of life and displacement of tens of thousands of Belgians that came with it. Belgium had every reason to fear that an eventual continuation of that war would again put them in the heart of the tornado, so to speak - as it did, a few years later. It hoped to avert that fate by declaring itself neutral at an early stage.

Excellent response! By the year 1936, 3 years before the outbreak of WW2, Belgium recognized that the German military build up was a danger to them. Since 1930, under the Wiemar Republic, Germany had begun to re- arm itself. Under the control of Hitler, this build up continued. Thus Belgium being aware of this declared in 1936, its neutrality.