Final answer:
Germany anticipated easy passage through Belgium based on the Schlieffen Plan but faced unexpected resistance. This invasion led to the British and French involvement, deviating from Germany's expectations and altering their initial swift victory plan.
Step-by-step explanation:
The Germans expected that when they approached Belgium en route to France at the beginning of World War I, they would be allowed to pass through easily. However, the Belgian King declined German passage, valuing Belgian neutrality and independence established by an 1839 treaty. As a result, Germany invaded Belgium and engaged in conflict with Belgian defenses, which disrupted their plan for a swift capture of France. The Schlieffen Plan had underestimated the strength of Belgian resistance and the quickness of British and French mobilization. The German advance through Belgium led to Britain's entry into the war, and although the Germans reached French territory, their initial strategy failed to deliver a quick victory, resulting in a prolonged trench warfare across the Western Front.
So, the German troops decided to go through Belgium at the beginning of World War I because they incorrectly assumed Belgium would not resist and that by bypassing the heavily fortified French border, they could more easily capture France. This belief contributes to the historical understanding of World War I strategies and the consequences of underestimating an opponent's willingness to defend their sovereignty.