[5] In 1917 he enlisted for the Armenian volunteer detachments and fought for General Dro in the Battle of Bash Abaran.

After the victory over the Ottoman forces and the establishment of the Democratic Republic of Armenia in 1918, Yerganian enlisted in Operation Nemesis, the covert operation led by a special body of the Armenian Revolutionary Federation aimed at assassinating all key organizers of massacres against Armenians both in the Ottoman Empire and in Azerbaijan.

[1][5] After Armenia lost its independence to the Bolsheviks, Yerganian went to Tbilisi where he and Misak Grigorian were assigned to assassinate former Prime Minister of the Democratic Republic of Azerbaijan Fatali Khan Khoyski and leader of the Musavat party Khan Mahmadov.

[2] After his task in Tbilisi was finished, Yerganian went to Istanbul where he attempted to recruit more avengers for the operation.

[2] Yerganian and Arshavir Shirakian were later given the task to assassinate both Cemal Azmi and Behaeddin Sakir who were in Berlin.