During World War I the Russian army mobilised more than 100 000 Estonian men, almost every tenth of whom was killed and every fifth wounded. Besides battle experience, the Estonians who fought at various fronts also acquired proper military instruction. The level of education, much higher than the average of the tsarist state, enabled men conscripted from Estonia to further their career, especially in the artillery and engineer corps. At the start of the world war the tsarist army had only 140 Estonian regular officers and 160 reserve ensigns; by 1918, however, over 2000 Estonian servicemen had become officers.

By the end of 1917, most of these men had gathered in Estonia and many of them formed the newly organised Estonian national units. During the revolution and general demoralisation process these men offered invaluable support to the idea of independent Estonia.

In November 1918 the German Empire collapsed and the Allied powers forced German army to pull back from the occupied regions. This also included the former territories of Russian Empire.

In Estonia, the provisional government seized power and tried to establish the Estonian Republic, proclaimed already at the eve of German invasion - on 24. February 1918.

Unfortunately, the young republic had no time to organise its forces before it was attacked by the Soviet Russia at the end of November. The Red Army sent a force of over 7000 men against Estonia, which had only some 2000 regular troops and a poorly armed and organised home guard - Estonian Defence League - units to counter the onslaught. The Republic's positions were also weakened by the Bolshevist propaganda that resulted in most of the Estonian population not being keen to fight for the republic and join the army.

The government called up the Estonians who had made a career in the Russian imperial army during the Great War, and pleaded for help from Scandinavian countries and Great Britain. The majority of volunteers, willing to join the army in November-December 1919, were 17-18 year old schoolboys, officers of former imperial Russian army, and intellectuals.

By early 1919, two thirds of Estonia was under Soviet control. Only with emergency help from the British fleet and volunteers from Finland, Denmark and Sweden was it possible to stop the Russians some 40 km from the capital city of Tallinn.

Changes in the organisation of Estonian defence forces, first victories and the knowledge that Estonia was not standing alone against the enemy allowed the start of a counteroffensive in the beginning of January 1919.

The Soviet regime also showed its true face to the population: as Tartu and Rakvere were freed by Estonian troops in mid-January, altogether around one hundred murdered priests, Baltic-German noblemen, intellectuals, farmers, students and their wives and children were found. Soviet terror had begun already in the first days of occupation, but gained momentum as the Bolsheviks were forced to retreat. The second big mistake the Bolsheviks made was not dividing the confiscated manor house lands between the farmers who had set their hopes on that. Instead, the Bolsheviks tried to establish big collective farms. The Estonian Republic, on the contrary, announced early on its readiness to undertake a radical land reform.

The land was liberated within three weeks. The breakthrough, however, came only with the mobilisation of all national resources. As a result the Estonian army had almost 90 000 men in the spring of 1919. The possibility to free the country and move the warfare on to the enemy's territory enabled to organise free elections and convene the Constituent Assembly already during the war, in April 1919. The Assembly passed the long-awaited land reform bill and the constitution.

In June and July of 1919, successful battles were conducted against the Baltic-German Landeswehr in northern Latvia (the victory at Cesis [Võnnu] on 23 June is commemorated by a national holiday, the Victory Day).

Military activity against Soviet Russia continued throughout autumn, and on 2 February 1920, the Tartu Peace Treaty was signed. Soviet Russia agreed to recognise the Republic of Estonia and pay war reparations.