The first World War started in July-August 1914. There were two major groups with many powerful countries involved. The countries were Germany, Austria-Hungary and Italy on one side and Great Britain, France and Russia on the other side.
Much before the war started, Germany had formulated Schlieffen Plan first in 1905 and modified it in 1911. The plan had assumed that if there was any outbreak of war in Europe, France would automatically join Russia and Germany would have to fight both of them in Western and Eastern Front. The plan had therefore proposed that the bulk of German forces were to be sent by train to Belgium and through Belgium to attack France, which was to be knocked out within first six weeks. After defeat of France, German forces were to be switched across to face Russia, whose army was supposed to be ready only after 6 weeks. The plan had also assumed that as France was defeated within first 6 weeks, Great Britain would not be able to land their armies on French territory and will not be able to help France.
Thus Germany could win the war on both Western and Eastern Front within 3-4 months. In actual practice Schlieffen Plan could not be carried out successfully.
When Germany invaded France through Belgium, it's armies took more than 2 weeks to pass over Belgium and reach the border of France due to very strong resistance from Belgian Army. This delay gave enough time to Britain to land it's armies on West Cost of France. Germany had planned under Schlieffen Plan to march to Paris both from Eastern and Western sides but due to British Forces on the Western Side, Germany could move towards Paris only though the Eastern Side. Although Germany made good progress initially and it's...