The Turks departed in 1426 , and he became even more desperate to form an alliance with Hungary .
The Ottomans responded with severe attacks that forced Tvrtko to accept their suzerainty and to agree to paying an annual tribute .
The Ottomans departed in 1426 , and he became even more desperate to form an alliance with Hungary .
The Ottomans responded with severe attacks that forced Tvrtko to accept their suzerainty and to agree to paying an annual tribute .