XVI
Murad did not set his army in motion against the Serbians immediately after the disaster at Plochnik. There was none of that feverish haste which had characterized his movements when he received the news of the Serbian and Hungarian crusade in 1363. For while the victory had aroused in the Balkan Christians a determination that they must drive the Osmanlis out of Europe, and a feeling that they could accomplish this end, its immediate result had been merely to repel the projected Ottoman invasion of Bosnia. Ali pasha disposed of sufficient forces to hold the conquests that had already been made. Murad had come to know the people with whom he was dealing. It was not so much to recruit his own army as to give the allies time to fall out with each other that Murad remained in Asia during the early months of 1388. To strike in the first flush of enthusiasm and buoyant hope would have brought him face to face with a united enemy. If he waited, he knew from past experience with the Balkan princes that the poison of jealousy would permeate the ranks of his ostensibly united enemies. The Osmanlis never made a mistake of judgement in dealing with Balkan alliances until the autumn of 1912.
Far from planning an offensive movement against the Serbians, Murad allowed Evrenos of Yanitza to lead a band of Ottoman mercenaries into the Morea, at the invitation of Theodore Palaeologos, to support the authority of the Byzantine Empire against the Frankish barons.[406] At the same time he ordered Ali pasha to cross the Balkans into northern Bulgaria.
Ali pasha started from Adrianople in the spring of 1388 with thirty thousand men to complete the conquest of Bulgaria. He crossed the Balkans by the pass north of Aïtos, which has ever since been called by the Osmanlis Nadir Derbend from the neighbouring town of Nadirkeuy.[407] Provadia was taken by surprise in the night. Shuman and the villages around it were next conquered. After an unsuccessful attack upon Varna, the Osmanlis retraced their steps through Provadia and Shuman, following the line of the modern railway from Varna to Sofia. Tirnovo, the ancient capital of Bulgaria, capitulated after a short struggle.
Sisman withdrew to the Danube through the valley of the Osma, and shut himself up in the fortress of Nicopolis. Owing to the ease of provisioning from the river side, it was impossible to starve him out. Ali pasha was compelled to call upon Murad, who had just crossed over from Asia to Thrace. When Murad arrived before Nicopolis, Sisman sued for peace. The conditions of Murad, that he pay the tribute due from the previous year and allow an Ottoman garrison to occupy the fortress of Drster as gage of future good conduct, were gladly accepted.
No sooner had Murad started southward than Sisman decided upon a final desperate resistance. He refused to give up Drster. But he had forgotten that Ali pasha was master of Shuman and the route to Varna. The Osmanlis took Drster by storm. Many villages along the Danube between Rustuk and Nicopolis fell into the hands of the Osmanlis. Ali pasha besieged Sisman for a second time in Nicopolis. The revelation of his own weakness and of the strength of the Osmanlis was a crushing blow to Sisman. He surrendered without conditions, and was taken, with his wife and children, to Murad’s camp. For reasons which the chroniclers do not indicate, Sisman was able to secure forgiveness and restoration to his former position as vassal prince of Bulgaria. But the Osmanlis were now installed in north-central Bulgaria up to the Danube River. Shuman and Nicopolis were Ottoman fortresses. Sisman had been rendered impotent to give effective aid in the great alliance.[408]