Warring parties :

Lithuanian Government : 

Augustinas Voldemaras, the first Prime Minister of Lithuania, did not consider the development of the military a priority and advocated Lithuanian neutrality.  He trusted that German mercenaries would protect Lithuania until peace could be made at the upcoming Paris Peace Conference . The residents organized local self-defense units. The first laws on the army were not issued until November 23. Some Lithuanians who had served in the Russian army during the World War returned to Lithuania and began to form battalions in Kaunas, Gardinas and Alytus . However, they lacked weapons, ammunition and officers.

By the end of December, with the Bolsheviks already in the country, Lithuania was left without leadership. Augustinas Voldemaras, Antanas Smetona , Chairman of the Council of Lithuania, and Martynas Yčas , Minister of Finance, traveled to Germany to request financial help. General Kiprijonas Kundratavičius , Deputy Minister of Defense, proposed a retreat to Gardinas and refused to command the Lithuanian defense. The first cabinet of ministers resigned on December 26, 1918. Mykolas Sleževičius took his place and organized a new government. On December 29, he published the first mass appeal in four languages ​​to recruit volunteers for the Lithuanian army. To recruit volunteers, he proposed land reform. This meant that the land would be taken from the large landowners and distributed first free of charge to the volunteers and then to the small farmers for a fee. 

German volunteers : 

In Berlin, Smetona and Yčas signed a loan agreement with Germany for 100 million marks . The money was used primarily to build up and supply the army. In addition, they negotiated direct German support in the war against the Soviets. Article 12 of the Armistice of Compiègne obliged the Germans to protect Lithuania from possible Soviet attacks , but Germany was also interested in maintaining its influence in the region and weakening Russia. At first, they tried to organize volunteers from the retreating soldiers of the German 10th Army under the command of General Erich von Falkenhayn . However, the soldiers were tired and demoralized and wanted to return home as soon as possible. Recruitment continued in Germany, particularly in Saxony . Volunteers were paid 30 marks per month plus 5 marks per day and had to commit for three months. The first Saxon volunteers, as they were called, arrived in Kaunas in early January, but some of them were deemed unfit and sent back. By the end of January, the German volunteers already numbered 4,000 men. 

Initially they were organized into the 46th Saxon Volunteer Division. On 22 February, Lieutenant General Walter von Eberhardt became their commander. In April and May, the German forces were reorganized into the South Lithuania Volunteer Brigade, which consisted of three regiments (18th, 19th and 20th) and a separate battalion in Raseiniai . The 18th Regiment fought on the side of the Lithuanians; the 19th Regiment guarded the Kaunas area and did not take part in the fighting; the 20th Regiment was stationed in Gardinas and then in Kėdainiai; the separate battalion joined the West Russian Liberation Army . The Baltic Landeswehr under the leadership of General Rüdiger von der Goltz organized a coup against the Latvian government and took Riga . On 23 May, in response to these events, the Paris Peace Conference called on Germany to withdraw its troops from both Latvia and Lithuania as soon as the local forces could defend themselves. The last Saxon volunteers left Lithuania in mid-July.

Soviets : 

On December 8, 1918, a revolutionary government composed of members of the Communist Party of Lithuania was formed, chaired by Vincas Mickevičius-Kapsukas . On December 16, the revolutionary government declared the establishment of the Lithuanian Soviet Socialist Republic . Between December 31, 1918 and January 1, 1919, the German garrison withdrew from Vilnius and transferred power over the city to a local Polish committee, contrary to the requests of the Lithuanian administration. The Lithuanian and Belarusian Self-Defense, which had allied itself with Poland, took over the posts. The Lithuanian government retreated to Kaunas, the provisional capital of Lithuania. On January 5, 1919, Vilnius was captured by the Soviets after a five-day battle with Polish paramilitary units led by General Władysław Wejtko . Mickevičius-Kapsukas and his government arrived in Vilnius from Daugavpils on 7 January.  On 27 February, the Lithuanian SSR was incorporated into the Lithuanian-Byelorussian Soviet Socialist Republic .

In the occupied territories, the Soviets created revolutionary committees and soviets modeled on the structures developed in Russia. Unlike other countries, Lithuanian communist organizations were young and had not yet developed a network of supporting local councils. They nationalized commercial establishments and large landholdings, with land to be used for collective farming rather than redistributed to smallholders. The Soviets propagated internationalism and atheism in a country with staunch Catholics and determined nationalists. The Soviets had support among the industrial working class, but in Lithuania it was too small. The Soviets demanded heavy war taxes from the conquered towns and villages. This policy alienated the local population and contributed to the Soviets’ eventual defeat. Mickevičius-Kapsukas was aware of the mood in the country, so in February 1919 he sent a telegram to Moscow warning that the conscription of Lithuanians into the Red Army would only encourage Lithuanians to volunteer for the Lithuanian army.

Soviet advance: 

Soviet troops (about 18,000–20,000 men) approached Lithuanian territory on 12 December 1918. About 5,000 of them were Lithuanians. The force consisted of three divisions. The divisions had no common military commander. Later, additional units were sent from Russia. The Soviets also recruited partisan groups behind the front lines. The Soviet soldiers were poorly supplied and had to rely on requisitioning food, horses and clothing from locals. Lithuania could not offer serious resistance, as its army at that time consisted of only about 3,000 untrained volunteers. Only local partisans, armed with weapons acquired from the retreating Germans, offered brief resistance.

The Red Army captured one town after another: Zarasai and Švenčionys (22 December), Utena (23 December), Rokiškis and Vilnius (5 January), Ukmergė and Panevėžys (9 January), Šiauliai (15 January), Telšiai (25 January). They thus controlled a third of Lithuania. The front stabilized somewhat when the Soviet troops were stopped near the Venta River by Latvian and German units (Baltic Landeswehr). The Germans also slowed the retreat of their troops after the Spartacist Uprising was crushed on 12 January. Southern Lithuania was somewhat better protected when the Germans withdrew from Ukraine via Gardinas. To avoid fighting between the retreating Germans and the Red Army, the Soviets and the Germans signed a treaty on January 18. In this treaty, a preliminary demarcation line was drawn, running through Daugai , Stakliškės and 10 km east of the Kaišiadorys – Jonava – Kėdainiai railway line . This prevented the Bolshevik forces from directly attacking Kaunas, the second largest city in Lithuania. The Red Army had to encircle Kaunas and attack via Alytus or Kėdainiai. The operation to capture Kaunas began on February 7.

Encirclement of Kaunas: 

Kėdainiai was attacked by just under 1,000 men. The Lithuanian troops from Panevėžys , commanded by Jonas Variakojis , and from Kėdainiai numbered only about 200 men. The Lithuanians resisted the Red Army advance at Kėdainiai and repelled it with German support. On 8 February, Povilas Lukšys was the first Lithuanian soldier to be killed in the war during a reconnaissance mission. On 10 February, Lithuanian and German troops jointly captured Šėta and forced the Red Army to retreat. The success of the operation boosted the morale of the Lithuanian army and prevented the Red Army from encircling Kaunas from the north.

On 9 February, the Soviet 7th Rifle Regiment (900 men) captured Jieznas, south of Kaunas. The Battle of Jieznas lasted three days, and after a setback caused by the betrayal of a Russian officer in Lithuanian service, the Lithuanians, with German support, finally won on 13 February and liberated Jieznas. The Soviets continued to push towards Kaunas. The 3rd and 4th Rifle Regiments (about 2,000 men) attacked Alytus on 12 February. The Germans did not engage in battle and retreated; the not yet fully trained 1st Lithuanian Infantry Regiment could not withstand the pressure of the Red Army and had to retreat towards Marijampolė and Prienai . On the night of 14–15 February, the German troops and a company of Lithuanians returned to Alytus and liberated the town. Kaunas was successfully defended and the front stabilized for a while. The Soviets were ordered to abandon the offensive and take a defensive position. This pause allowed the Lithuanians to better organize and train the volunteers.