When World War I broke out in 1914, the Russian Empire had the world's largest standing army, with approximately 1,400,000 soldiers on active duty. The Russian Army bore the brunt of the fighting on the Eastern Front and also saw action on the Balkan Front and the Western Front.

Russian Reserves

In addition to having the world's largest standing army, the Russian Empire had vast military reserves. As a result, Russia was able to mobilize more than 5,000,000 troops at the beginning of World War I. Russia also boasted the world's largest air force in 1914, with more than 360 aircraft. By the time Russia petitioned for peace in 1917, nearly 15 million Russians had served. Although Russia had vast human resources to put towards the war effort, military effectiveness was hindered by the fact that Russia didn't have enough rifles for all soldiers.

Heavy Losses

A combination of inadequate war material, lack of training, a shortage of experienced officers and poor roads and railroads caused the Russian Army to suffer heavy losses in the early years of the war. Russia lost two entire divisions in four days of fighting at the Battle of Tannenberg in August, 1914. Russia would endure more than two million casualties in 1915 en route to leading all nations involved in numbers of wounded – 2.8 million – and prisoners of war – 2.4 million. Russia's 1.8 million war deaths were second only to Germany's 1.95 million.

Russian Revolution

The heavy Russian losses suffered during World War I, combined with food shortages, furthered civil unrest already been brewing in Russia. The Russian Army lost more soldiers to desertion – more than two million by some estimates – than comprised the entire armies of several countries fighting in the war. Many of these deserters joined revolutionary movements within Russia. With the war going poorly and Russia in a state of civil unrest, Czar Nicholas II abdicated on March 15, 1917. In October of that year, the Bolsheviks – a communist revolutionary group – seized power in Russia.

The Red Army

After seizing power, the Soviet government of Russia issued a decree of peace on Oct. 26,1917. Leon Trotsky, a prominent member of the Communist Party of Russia, was sent to negotiate peace terms with the Central Powers. This culminated in the Brest-Litovsk Treaty, which cost Russia the Ukraine, Finland, the Caucasus, Poland and their Baltic provinces. The Soviet government demobilized the Russian Army in 1918 and formed the Red Army, which restored troop numbers to more than 5,000,000 in the years immediately following Russia's involvement in World War I.