Initially, the Ottoman invasion was not considered as a significant threat by both Bulgarians and Byzantines. For only one decade between 1354 and 1364 the Ottomans conquered virtually the whole of Thrace seizing large cities such as Plovdiv, Beroia, Dianopolis (Yambol) and Adrianople and defeating several small Bulgarian forces. The centuries-old mistrust between Bulgarians and Byzantines spoiled the negotiations between the two empires for an alliance and even led to the last Byzantine-Bulgarian war in 1364. In 1371 a large Bulgarian-Serb army under Vukašin Mrnjavčević and Jovan Uglješa, two feudal lords in Macedonia, was annihilated by the Ottomans under Lala Shahin Pasha at Chernomen and soon the Bulgarian Emperor had to admit the defeat and became a vassal to the invaders. Numerous Bulgarian fortresses in the Rhodope mountains, Sofia valley and eastern Bulgaria were captured one by one over the next twenty years. In 1393 the capital Tarnovo was besieged and seized by the Ottoman Turks and three years later fell Vidin – the last major Bulgarian city. Resistance to the invaders continued until 1422 when the country was fully conquered. The Ottoman invasion was a disaster for the Bulgarian army — the nobility and the leaders of the nation were killed or emigrated and civilians were not allowed to have weapons until the 19th century.