Michael Palaiologos found himself faced with a powerful coalition that, according to the Byzantinist Donald Nicol, "seemed likely to threaten the possession not only of Thessalonica but even of Constantinople itself".
Michael Palaiologos did not tarry.
Already in the autumn of 1258, his army crossed over into Europe, under his brother the sebastokrator John Palaiologos and the megas domestikos Alexios Strategopoulos, and wintered in Macedonia, where it was joined by local levies.
At the same time, Michael Palaiologos sent separate embassies to each of the three main allies, hoping to pry them apart by diplomacy.
These efforts failed, as the three allies stood to gain much from a successful offensive against Nicaea.

In spring 1259, the Nicaeans went on the offensive, and advanced quickly westwards along the Via Egnatia.
Michael II of Epirus, who was encamped at Kastoria, was caught off guard by the rapidity of their advance, and when the Nicaeans crossed the pass of Vodena to face him, he was forced to hastily retreat with his troops across the Pindus mountains to the vicinity of Avlona, held by his ally Manfred.
There the final negotiations for the marriage between Manfred and Helena were concluded: the wedding took place at Trani on 2 June 1259.
In their retreat, which continued even during night, the Epirotes reportedly lost many men in the dangerous mountain passes, while the Nicaean generals captured Ohrid and Deavolis and other cities.
Michael Palaiologos found himself faced with a powerful coalition that, according to the Byzantinist Donald Nicol, "seemed likely to threaten the possession not only of Thessalonica but even of Constantinople itself". Michael Palaiologos did not tarry. Already in the autumn of 1258, his army crossed over into Europe, under his brother the sebastokrator John Palaiologos and the megas domestikos Alexios Strategopoulos, and wintered in Macedonia, where it was joined by local levies. At the same time, Michael Palaiologos sent separate embassies to each of the three main allies, hoping to pry them apart by diplomacy. These efforts failed, as the three allies stood to gain much from a successful offensive against Nicaea. 
In spring 1259, the Nicaeans went on the offensive, and advanced quickly westwards along the Via Egnatia. Michael II of Epirus, who was encamped at Kastoria, was caught off guard by the rapidity of their advance, and when the Nicaeans crossed the pass of Vodena to face him, he was forced to hastily retreat with his troops across the Pindus mountains to the vicinity of Avlona, held by his ally Manfred. There the final negotiations for the marriage between Manfred and Helena were concluded: the wedding took place at Trani on 2 June 1259. In their retreat, which continued even during night, the Epirotes reportedly lost many men in the dangerous mountain passes, while the Nicaean generals captured Ohrid and Deavolis and other cities.
Battle of Pelagonia