The Finnish Civil War, a part of the national and social turmoil caused by the First World War (1914-18) in Europe, is fought in Finland from January 27 to May 15, 1918, between the forces of the Social Democrats led by the People's Deputation of Finland, commonly called the "Reds" (punaiset), and the forces of the non-socialist, conservative-led Senate, commonly called the "Whites" (valkoiset).

The Reds are supported by Bolshevist Russia, while the Whites receive military assistance from the German Empire.Defeat in World War I and the February and October Revolutions in 1917 had caused a total collapse of the Russian Empire, and the destruction in Russia had resulted in a corresponding breakdown of Finnish society during 1917.

The Social Democrats on the left and conservatives on the right compete for the leadership of the Finnish state, which had shifted from the left to the right in 1917.

Both groups collaborate with the corresponding political forces in Russia, deepening the split in the nation.As there have been no generally accepted police and army forces to keep order in Finland after March 1917, the left and right have begun building security groups of their own, leading to the emergence of two independent armed military troops, the White and Red Guards.

An atmosphere of political violence and fear grows among the Finns.

Fighting breaks out during January 1918 due to the acts of both the Reds and Whites in a spiral of military and political escalation.

The Whites are victorious in the ensuing war.

In the aftermath of the 1917–18 crisis and the Civil War, Finland passes from Russian rule to the German sphere of influence.

The conservative senate attempts to establish a Finnish monarchy ruled by a German king, but after the defeat of Germany in the First World War, Finland emerges as an independent, democratic republic.

The Civil War remains the most controversial and emotionally loaded event in the history of modern Finland, and there have even been disputes about what the conflict should be called.

Approximately 37,000 people die during the conflict, including casualties at the war fronts and deaths from political terror campaigns and high prison camp mortality.

The turmoil destroys the economy, splits the political apparatus, and divides the Finnish nation for many years to come.

The country will be slowly reunited through the compromises of moderate political groups on the left and right.