Finnish Civil War: A group of Red Guards hangs a red lantern atop the tower of Helsinki Workers' Hall to symbolically mark the start of the war.

The Red Guards (Finnish: Punakaarti, Swedish: Rda gardet) were the paramilitary units of the Finnish labour movement in the early 1900s. The first Red Guards were established during the 1905 general strike, but disbanded a year later. After the Russian 1917 February revolution the Red Guards were re-established and in the 1918 Finnish Civil War they formed the army of Red Finland. The combined strength of the Red Guard was about 30,000 at the beginning of the Civil War, peaking at between 90,000 and 120,000 during the course of the conflict. The number included more than 2,000 members of the Women's Guards. In May 1918, up to 80,000 Reds were captured by the victorious Whites, 12,000 to 14,000 of them died in the prison camps due to execution, disease and malnutrition. A majority of the Reds were finally pardoned in late 1918.

Approximately 10,000 to 13,000 Reds managed to flee to Soviet Russia. Some of them fought in the Russian Civil War until 1920 against the Finnish Whites invading East Karelia. The Murmansk Legion was a British-organized military unit composed of the Red Guard members from Northern Finland who had fled to Russia in the early stages of the Finnish Civil War.

The Finnish Civil War was a civil war in Finland in 1918 fought for the leadership and control of the country between White Finland and the Finnish Socialist Workers' Republic (Red Finland) during the country's transition from a grand duchy of the Russian Empire to an independent state. The clashes took place in the context of the national, political, and social turmoil caused by World War I (Eastern Front) in Europe. The war was fought between the "Reds", led by a section of the Social Democratic Party, and the "Whites", conducted by the conservative-based senate and the German Imperial Army. The paramilitary Red Guards, which were composed of industrial and agrarian workers, controlled the cities and industrial centers of southern Finland. The paramilitary White Guards, which consisted of land owners and those in the middle- and upper-classes, controlled rural central and northern Finland, and were led by General C. G. E. Mannerheim.

In the years before the conflict, Finland had experienced rapid population growth, industrialisation, pre-urbanisation and the rise of a comprehensive labour movement. The country's political and governmental systems were in an unstable phase of democratisation and modernisation. The socio-economic condition and education of the population had gradually improved, and national thinking and cultural life had increased. World War I led to the collapse of the Russian Empire, causing a power vacuum in Finland, and the subsequent struggle for dominance led to militarisation and an escalating crisis between the left-leaning labour movement and the conservatives. The Reds carried out an unsuccessful general offensive in February 1918, supplied with weapons by Soviet Russia. A counteroffensive by the Whites began in March, reinforced by the German Empire's military detachments in April. The decisive engagements were the Battles of Tampere and Vyborg, won by the Whites, and the Battles of Helsinki and Lahti, won by German troops, leading to overall victory for the Whites and the German forces. Political violence became a part of this warfare. Around 12,500 Red prisoners died of malnutrition and disease in camps. About 39,000 people, of whom 36,000 were Finns, died in the conflict.

In the immediate aftermath, the Finns passed from Russian governance to the German sphere of influence with a plan to establish a German-led Finnish monarchy. The scheme ended with Germany's defeat in World War I, and Finland instead emerged as an independent, democratic republic. The civil war divided the nation for decades. Finnish society was reunited through social compromises based on a long-term culture of moderate politics and religion and the post-war economic recovery.

The Finnish Civil War of 1918 was the second civil conflict within Finland's borders, as the Cudgel War of 1596-1597 (where poor peasants rose up against the troops, nobles and cavalry who taxed them) has similar features.