Why did Frederick II fail to turn the victory at Cortenuova into lasting control of northern Italy?

Although Frederick II achieved a significant military victory over the Lombard League at the Battle of Cortenuova in 1237, he failed to translate this success into lasting control of northern Italy for several key reasons:

• Resilient Resistance: Major cities, most notably Milan, refused to submit and continued to hold out against imperial authority. Frederick’s subsequent failure to capture Brescia in 1238 further stalled his momentum.12
• Papal Conflict: The victory intensified the rift with Pope Gregory IX, who excommunicated Frederick and actively mobilized opposition against him. The papacy viewed Frederick’s expansion as a threat to the Papal States and the rights of the church, effectively turning the political struggle into a broader ideological and propaganda war.12
• Political Instability: Frederick’s reliance on local tyrants, such as the da Romano family, alienated former allies and created local instability. Furthermore, the emperor was frequently distracted by the need to manage his other domains and address the growing threat of the papacy, which prevented him from focusing exclusively on consolidating his northern Italian gains.12