During this war, the Yser River was flooded at its mouth on the North Sea to prevent enemy  advances.
During this war, the Yser River was flooded at its mouth on the North Sea to prevent enemy  advances. That battle came a month after the 9th Army under Ferdinand Foch liberated  Chalons, after which both armies fought over the Belgian town of (*) Ypres, ending the "race to  the sea." Fighting near the Marne River gave way to trench warfare in, for 10 points, what war  between the Allies and Central Powers ended by the Treaty of Versailles in 1918?
During this war, the Yser River was flooded at its mouth on the North Sea to prevent enemy  advances.
World War I or the First World War (prompt on the Great War, the War to end all Wars,  and other such superlative names)