Throughout the 1870s, Greece kept pressure on the Ottoman Empire, seeking territorial expansion into Epirus and Thessaly. The Russo-Turkish War of 1877–1878 provided the first potential alliance for the Greek kingdom. George's sister Dagmar was the daughter-in-law of Alexander II of Russia, and she sought to have Greece join the war. The French and British refused to countenance such an act, and Greece remained neutral. At the Congress of Berlin convened in 1878 to determine peace terms for the Russo-Turkish War, Greece staked a claim to Crete, Epirus and Thessaly.