Fourteenth-century Peloponnese was made up of several Latin states and dominant Venetian colonies, remnants of the Fourth Crusade; the only Byzantine territory was the Despotate of Morea. Its rulers, the despots, always trusted kinsmen of the emperor, followed the policies of Constantinople while trying to carve a separate political and diplomatic path. The protagonist of this paper is Theodore I Palaeologus (1382-1407), brother of the emperor Manuel II (1391-1425). Through the observation of his reign in Morea, the reader can take a glimpse at the empire’s situation at the time, which was defined by the irreversible expansion of its enemies and the on-going dynastic struggles that led to the political, social and economic collapse of the Byzantine state. Upon his arrival, Theodore had to cope with the rebellious Byzantine ruling class, who preferred their independence instead of abiding to the beadings of the central administration. That problem, still present until his death, forced him to make sporadic compromises and superficial coalitions, usually without benefit. Among his Latin allies were Nerio Acciaiuoli, the despot’s father-in-law, Venice and the Hospitallers of Rhodes. Besides the Latins, whose help proved inadequate, Theodore turned to the swiftly rising Ottoman sultans. Although at first, the Ottomans suppressed the internal opposition of the despot, soon they became the most significant threat, not only for the Peloponnese, but for the rest of the failing Byzantine Empire. In the long run, Theodore, from an “ally” of Murād I (1361-1389), turned out to be a liegeman of Bāyezīd I (1389-1402). This study, based on contemporary Byzantine sources and modern bibliography, aims to roughly present Theodore’s foreign affairs and his co-existence in the Peloponnese with the Latins and the Ottoman Turks, either as friends or as foes.