Complex sentence: After the victory the Bulgarians retook most of Thrace, including the important city of Philippopolis but the unexpected Bulgarian successes made the Byzantine nobility to plot against Kaloyan and ally itself with the Latins.
Split into simpler sentences: After the victory, the Bulgarians retook most of Thrace, including the important city of Philippopolis. The unexpected Bulgarian successes caused the Byzantine nobility to plot against Kaloyan and ally themselves with the Latins.