The party also played role in establishment of Democratic Republic of Armenia , as party members took part in the Battle of Sardarapat , during the World War I at Caucasus Campaign , which defended the Armenian capital of Yerevan from Army of Islam of Ottoman Empire . The party also played role in establishment of Democratic Republic of Armenia , as party members took part in the Battle of Sardarapat , during the World War I at Caucasus Campaign , which defended the Armenian capital Yerevan from the Army of Islam of the Ottoman Empire .