First, be aware that the Russian Revolution itself was closely tied with the experience of World War I. Russia was suffering deeply in the experience of the war. According to one historian's statistical record, out of approximately 18 million troops mobilized, Russia faced over fifty per-cent casualties, with 1.8 million dead, almost 5 million wounded, and over 2 1/2 million either taken prisoner or gone missing (statistics courtesy of John Merriman, A History of Modern Europe, 3rd edition (New York: W. W. Norton, 2010), p. 924. Merriman himself cites another historian, J. M. Winter). At the same time, the experience of the war was creating severe food shortages at home.

This resulted in the Russian Revolution, with Tsar Nicholas II abdicating and a new provisional government set in place. However, the provisional government made the decision to continue the war, which helped the Bolsheviks launch a second revolution against the Provisional Government. After the Bolsheviks took over the government, they signed the Treaty of Brest-Litovsk, pulling Russia out of the First World War.

Russia withdrew from World War I because the Bolsheviks, who had promised the Russian people "peace, land, and bread," came to power after overthrowing the provisional government. This provisional government, headed by moderates, had seized power from Tsar Nicholas, forcing him to abdicate in March of 1917. But the provisional government failed to remove Russia from the war, angering many, especially workers in Petrograd, the imperial capital. Led by Vladimir Lenin, the radical Bolsheviks launched a revolution in late 1917 that overthrew the provisional government, giving power to revolutionary committees known as soviets, and withdrawing Russia from the war. With a civil war between the Bolsheviks and a coalition of their enemies raging, the Treaty of Brest-Litovsk formalized Russia's exit from the war in 1918. The treaty was later negated by Germany's surrender later in that year, but the Russians, whose civil war dragged out until 1921, did not participate directly in the peace process that followed.

The short answer is that the triumph of the Bolshevik revolutionaries inside Russia led to the end of the Russian involvement in the war. When the communists took over in 1917, they decided that the highly unpopular and destabilizing war was sacrificing the working classes for the financial interests of the wealthy. Therefore, they withdrew Russia from World War I.

However, it was the mismanagement of the war effort by the Czar and other high officials that led to a situation in which the communists could take over the government. The Russians, who had been defeated militarily by the Japanese in 1905—a surprise loss—were unprepared to enter the war in 1914. While war could have been an opportunity to pull the country together in patriotic union, the defeats the Russians experienced and the sufferings on the home front tore the country apart.

Food shortages meant that both troops and people at home were going hungry. High war casualties upset people. Ordinary citizens, looking for a scapegoat, turned on the Czar's wife, Alexandria, as a traitor to Russia who was actually working for the enemy. All this led to a breakdown of faith in the Czar's leadership that led in turn to a communist takeover, Russian withdrawal from the war, and then a civil war.

Russia's withdrawal from World War I was essentially the result of its inadequate leadership in the early stages of the war. Czar Nicholas, who was very inexperienced as a political leader, and even more so as a military commander, insisted on taking a direct role in the military command of the war. The entry into the Great War came at a time of great economic and political instability in Russia. The war also came soon after their defeat at the hands of Japan, which demonstrated that its military capabilities were falling behind. Despite these signs that Russia was not prepared for a modern conflict, Russia hastily entered the war on the side of the Allied Powers.

The early losses to Germany in World War I intensified the economic and political problems that already existed in Russia. With each loss on the battlefield, the Czar lost more credibility. He was replaced by a democratic government in the spring of 1917. The Provisional Government decided to keep fighting in World War I at its own peril. When the communists emerged as the political authority after the October Revolution, they decided that the war was a capitalist affair and promptly withdrew from the combat.

Why did Russia withdraw from the First World War?

1). The Bolsheviks came to power. One of the biggest mistakes of the Provisional Government that took power in the February Revolution of 1917 was that it continued Russia's involvement in a war that was widely unpopular. Russia had sustained enormous losses during World War One without much in the way of territorial gain.

When the Tsar was overthrown, many Russians believed that the country would pull out of the war. That this didn't happen played into the hands of the Bolsheviks, who'd been opposed to the war from the start, seeing it as nothing more than a quarrel between the crowned heads of Europe that had nothing to do with the working classes.

After the Bolsheviks took power in October 1917, they immediately set to work disengaging Russia from the war, eventually signing the Treaty of Brest-Litovsk, which ceded vast territory to Germany in return for Russia withdrawing from the conflict.

2). The war was deeply unpopular. As we have seen, Russia didn't seem to get much out of its involvement in the war. More than most of the participants, Russia was greatly impoverished by the conflict, enduring chronic shortages on the home front for very little strategic gain. The Bolsheviks skillfully exploited the war's unpopularity, and by making themselves the most consistently anti-war party, they put themselves in a prime position to stage an armed insurrection against the Provisional Government.

3). The fall of the Romanovs. The fall of the Russian royal family, after more than 300 years on the throne, spelled the end of Russia's involvement in the war. This did not happen immediately, of course; as we've seen, the Provisional Government made the huge mistake of keeping Russia in the war. But without the autocratic system of Tsarist government in place, it was inevitable that Russia would withdraw from the war at some point.

Initial Russian involvement in World War One was based on a sense of cultural solidarity with the Serbians, who were fellow ethnic Slavs. The Tsar, like all his predecessors, saw himself as the protector of fellow Slavs, wherever they were, so Tsarist Russia didn't hesitate to join the war when it broke out.

However, once the Tsar had been deposed, that imperative no longer held. The Provisional Government had neither the inclination nor the ability to take up the mantle of pan-Slavism, so the original reason for Russia's involvement in the war was no longer valid. That the Provisional Government was unable to supply a compelling alternative justification was its undoing.