growing militarism which led to an arms race between the powers. As a result of the arms race, all European powers were ready for war and had time tables that would send millions of reserves into combat in a matter of days. France was bound by treaty to defend Russia. Austria-Hungary had declared war on Serbia due to the Black Hand's assassination of Archduke Ferdinand, which acted as the immediate cause of the war. France was brought into the war by a German declaration of war on August 3, 1914. The Pre-War Army and mobilization In common with most other continental European powers, the French Army was organized on the basis of universal conscription. Each year, the "class" of men turning twenty-one in the upcoming year would be inducted into the French Army and spend three years in active service. After leaving active service they would progress through various stages of reserves, each of which involved a lower degree of commitment. Active Army (20–23) Reserve of the Active Army (24–34) Territorial Army (35–41) Reserve of the Territorial Army (42–48) The peacetime army consisted of 173 infantry regiments, 79 cavalry regiments, and 87 artillery regiments. All were substantially under strength and would be filled out on mobilization by the first three classes of the Reserve (that is, men between 24 and 26). Each regiment would also leave behind a cadre of training personnel to conduct refresher courses for the older reservists, who were organized into 201 Reserve Regiments and 145 Territorial Regiments. Above the regimental level, France was divided into 22 Military Regions, each of which would become an Army Corps on mobilization. At the apex of the French Army was the General Staff, since 1911 under the leadership of General Joseph Joffre. The General Staff was responsible for drawing up the plan for mobilization, known as Plan XVII. Using the railroad network, the Army would be shifted from their peacetime garrisons throughout France to the eastern border with Germany. The order for mobilization was given on 1 August 1914, the same day that Germany declared war on Russia. Immediately called to their regiments were the classes of 1896 to 1910, comprising almost three million reservists of 24 to 38 years old. Organization during the war Upon mobilization, Joffre became Commander-in-Chief of the French Army. Most of his forces were concentrated in the northeast of France, both to attack Alsace-Lorraine and