In 1403, following Tamerlane's devastation on Turkish Anatolia, Suleiman had to temporarily focus on securing his empire in Asia, leaving the European Ottoman possessions open to attack. Now, at the time Manuel II was in northern Italy, and visited Genoa and Venice to propose an alliance to take advantage of the Ottoman's setbacks.
To stop the alliance from forming, Suleiman ceded Thessaloniki, the Thracian seaboard, and some islands to the Byzantines, and the emperor, satisfied, didn't form a coalition to take advantage of Tamerlane's invasion.
WI Suleiman doesn't pacify the Byzantines and Venetians by ceding land, and an anti-Turk coalition of Genoese, Venetians, Byzantines, and crusader Latins attack Ottoman Rumelia at its most vulnerable?