Neutrality: A policy or status of a nation that does not participate in a war between other nations. Belgium had declared neutrality before being invaded by Germany during WWI.
Schlieffen Plan: A German strategic plan for victory in a possible two-front war against France (to west) and Russia (to east). It involved marching through neutral Belgium into northern France.
Treaty of Versailles: The treaty imposed on Germany by Allied powers in 1920 after the end of World War I which demanded exorbitant reparations from the Germans.