Starting in the 15th century the Ottoman Empire began to expand at the expense of the Byzantine Empire and other countries friendly to Genoese merchants. The gradual loss of Imperial territory, coupled with the destruction of smaller Christian states such as Trebizond, Cyprus, and Amasra chipped away at Genoese mercantile interests in the Black Sea. The Ottomans constructed a massive fleet, and in doing so became the dominant naval power in the Eastern Mediterranean. In 1453 Constantinople fell, and the Ottomans closed the Dardanelles and Hellespont to Christian shipping. This act cut the Genoese navy off from its bases in the Black Sea, and Genoa found itself isolated from the colonies that had for centuries provided the republic access to Russia and Central Asia. With no way to return home and having had their lines of communication disrupted, the Genoese squadron in the Black Sea dispersed. Now indefensible, warehouses, fortresses, and ships built by the republic were lost. The former Genoese colonies were eventual annexed by regional powers, with Kaffa falling to the Ottomans in 1475.