After the assassination of Danilo I on 13 August 1860, Nikola I, the nephew of Danilo, became the next ruler of Montenegro. Nikola sent aid to the Serb rebels in the Herzegovina Uprising (1875–78), and then led a war against the Ottomans, the Montenegrin–Ottoman War (1876–78). The advancement of Russian forces toward Turkey forced Constantinople to sign a peace treaty on 3 March 1878, recognising the independence of Montenegro, as well as Romania and Serbia, and also increased Montenegro's territory from 4,405 km² to 9,475 km². Montenegro also gained the towns of Nikšic, Kolašin, Spuž, Podgorica, Žabljak, Bar, as well as access to the sea. This was the Great Powers' official demarcation between Montenegro and the Ottoman Empire, de facto recognizing Montenegro's independence; Montenegro was recognized by the Ottoman Empire at the Treaty of Berlin (1878). The first Montenegrin constitution (also known as the Danilo Code) was proclaimed in 1855. Under Nicholas I (ruled 1860–1918), the principality was enlarged several times in the Montenegro-Turkish Wars and was recognised as independent in 1878. Nicholas I established diplomatic relations with the Ottoman Empire. Minor border skirmishes excepted, diplomacy ushered in about 30 years of peace between the two states until the deposition of Abdul Hamid II in 1909.