Germany's generals had decided that the best way to defeat France was to go through Belgium using a plan called the "Schlieffen Plan". This was invented by the German Army Chief of Staff, Alfred Von Schlieffen. They could then attack the French army at the north side and the south side at the same time. The German Army went into Belgium on August the 4th. On the same day, Great Britain started a war on Germany, because Britain was a friend of Belgium. The British had said some time before, in 1839, that they would not let anyone control Belgium, and they kept their promise.