That vassal state is the personal domain of Nikolaos Glabas, the Exarkhate of Thessalonika. He had been defacto ruler of the West since 1301, but only became a de jure autonomous vassal in 1308 in exchange for handing over Simeon II. Thessalonika would under most circumstances be crushed, but lying a mere five miles across the border are the mines that produce ~70% of the empire's gold. In a single day, Glabas could cripple the empire indefinitely if he chose to. And so now, the two sides wait.