Location map of Belgium with an indication of the Western front and Western Flanders.

The assassination of Archduke Franz Ferdinand in Sarajevo on 28 June 1914 was the start of a series of events, in which several countries were involved. This culminated in the First World War. When France announced the war against Germany on the 3rd of August, the Germans invaded neutral Belgium on the 4th of August, seeking to reach Paris by the shortest possible route. Britain declared war against Germany on that same day. The British were obligated to defend neutral Belgium by the terms of a 75-year old treaty. With Britain's entry into the war, her colonies and dominions abroad variously offered military and financial assistance, and included Australia, Canada, India, New Zealand and the Union of South Africa. The United States entered the war on 6 April 1917. All these countries became active in and around the Ypres Salient.