The representatives of the workers’ movement, who had remained a minority in Parliament and were frustrated by their inconsiderable parliamentary influence, organized a revolution on the 27th of January, 1918, following the example of the Russian revolution in October. They managed, supported by Russian troops, to occupy the southern part of the country. This ignited the Civil War. The power of the Senate was concentrated in Vaasa and that of the People’s Delegation, established by the revolutionaries, in Helsinki. Owing to the war, the parliament was inoperative.

Throughout the autumn of 1917, the political crisis had been spurred by the formation of armed civil organizations. The independence men and those supporting the traditional order founded Civil Guards or white guards (called "butcher guards" by their opponents), and the different movements among the workers "order guards" or Red Guards. The government took pains to strengthen national order in place of these organizations, and in January 1918, the parliament granted the government the right to establish firm order, which led to the accusation by the workers of limiting their civil rights.

From the very beginning, the Soviet Government took the side of the revolutionary government in Finland, and was ready to offer military aid to the reds, provided the war would end rapidly. There was an imminent danger that the protraction of the war would risk German intervention. German pressure in February and March 1918, compelled the Soviet Government to give up public aid to the Finnish reds. The relations between Russia and red Finland were settled in the so-called Red Convention on the first of March. This convention proved that the reds strove to maintain national independence and even to create national greatness, but Lenin forced the Finnish reds to accept the name, the Socialistic Republic of Finland. At that point, the interest of the whites began to be directed to eastern Karelia.

The German troops arrived in Åland in early March and the offensive of the German Baltic division extended to the mainland in early April, and eventually resulted in taking Helsinki on the 15th of April. Despite this auxiliary expedition, Finland remained formally neutral in regard to the parties of the First World War, but was forced to submit her finances to German supervision.

The Russian troops, continuously stationed on Finnish soil, fought alongside the white Finns, but the Germans were eager to see them leave and worked to this effect through pressure and negotiations. The exit of the Russian Baltic Navy from Helsinki harbour through icy waters to Kronstadt in March and April took place in accordance with the agreement. In April and May 1918 the whites were besieging the Ino Fort, ceded to Russia by the red People’s Delegation, and finally in the middle of May the Russians left the ruined fort in the hands of the whites.

Since Mannerheim, as the Commander-in-Chief, did not take a sufficiently firm attitude towards the revengeful actions of his troops against the revolutionaries – so-called white terrorism – his name was linked both with the executions of the reds and the catastrophic malnutrition in the prison camps. He was named "butcher general" by the reds. For socialists, his background denoted reactionism and the commandership of the whites bloody memories. Historians regard the bureaucratic investigation method, insisted by the Senate, as the reason for white terrorism.

At the close of the war operations in May 1918, the Soviet Government agreed to negotiate peace with the Finnish government through German mediation. It was not until spring 1920 that the negotiations were

reopened, and the Tartu Peace Treaty was signed in October 1920.

For Mannerheim, the war of 1918 was expressly a war of liberation. From his European point of view, the rebellion started by the People’s Delegation was only one instance in the wave of revolutions and anarchy, which spread from Russia and which threatened the independence of Finland. He wanted to preserve the neutrality of the independent country, and regarded German military assistance as a weakening factor, which should be kept within certain limits. He pressed forward with the occupation of Tampere to show that the Finns were able to handle the situation by their own exertions before the arrival of German aid.