He participated in the smuggling of the banned Lithuanian publications, organized protests during the Russian Revolution of 1905, and was one of the co-founders of the Peasant Union.

During World War I, he was drafted into the Imperial Russian Army and worked as a doctor at various military hospitals.

Alseika lived and worked in Vilnius which was bitterly contested between the interwar Lithuania and the Second Polish Republic.

There he was a member of a secret group of Lithuanian students led by the future writer Jonas Biliūnas.

[2] During the Russian Revolution of 1905, he organized protests among the peasants and workers near Vilnius, Trakai, Švenčionys agitating them to strike and resist Tsarist officials.

After the outbreak of World War I, he managed to return to Lithuania and was drafted into the Imperial Russian Army.

The society then used the funds to purchase equipment and other inventory of the war hospital and relocated it to Vilnius in July 1918.

On 5 December 1918, he as a representative of the Lithuanian Popular Peasants' Union was coopted by the Council of Lithuania.

[1] After the return, he withdrew from political and party work devoting his energy to the affairs of the Lithuanians in Vilnius Region.

[9] Alseika sought to ally with other ethnic minorities in Poland (Belarusians, Ukrainians, Jews).

[11] He was also an active member of the Lithuanian Scientific Society[1] and briefly was its acting chairman after the death of Jonas Basanavičius in February 1927.

He also published books about Lithuanian national aspirations (Lietuvių tautinė idėja istorijos šviesoje in 1924) and conditions of Lithuanians in Vilnius Region (Vilniaus krašto lietuvių gyvenimas 1919–34 in 1935)[1] as well as two historical books on Grand Duke Vytautas (in 1924 and 1927).

[15] The authorities wanted to deport Alseika and his wife in May 1924, but it was avoided after a complaint to the Human Rights League in Paris.

[16] The Polish government attempted to deport Alseika again in spring 1927, but the Secretary-General of the League of Nations intervened.

[17] In 1910, Alseika married fellow physician Veronika Janulaitytė who specialized in ophthalmology (eyes).