Why ace was captured by megallan?

Portgas D. Ace was captured by Admiral Akainu (Sakazuki) during the Marineford War after he confronted him while trying to protect his brother, Monkey D. Luffy. Ace, a former commander of the Whitebeard Pirates, was ultimately betrayed by his own decision to engage in a fight against Akainu, who provoked him by insulting Whitebeard. His capture was part of a larger plan by the Marines to eliminate powerful pirates and maintain control over the seas. Ace's execution was intended to serve as a warning to others and to assert the Marines' dominance.