Germany presented an ultimatum to Russia to demobilize, and when this was refused, declared war on Russia on 1 August. Being outnumbered on the Eastern Front, Russia urged its Triple Entente ally France to open up a second front in the west. Earlier in 1870, the Franco-Prussian War had ended the Second French Empire and France had ceded the provinces of Alsace-Lorraine to a unified Germany. Bitterness over that defeat and the determination to retake Alsace-Lorraine made the acceptance of Russia's pleased for help an easy choice, so France began full mobilization on 1 August and, on 3 August, Germany declared war on France. The border between France and Germany was heavily fortified on both sides so, according to the Schlieffen Plan, Germany then invaded neutral Belgium and Luxembourg before moving towards France from the north, leading the United Kingdom to declare war on Germany on 4 August due to their violation of Belgian neutrality.…