Benghazi is Libya’s second-largest city, and is the capital of Cyrenaica (the country’s eastern region). The city was the epicenter of protests against Libyan dictator Muammar Qaddafi during the 2011 Arab Spring uprising and subsequently served as the de facto headquarters of the anti-Qaddafi rebellion.
In fact, it was Qaddafi’s near-reconquest of Benghazi that prompted the Western intervention in the Libyan civil war on March 18, 2011. That intervention, roughly a month after the anti-Qaddafi uprising began, ended after Western-supported rebel forces took the capital of Libya, Tripoli, on August 22 of that year. Tripoli was Qaddafi’s final stand, and his regime collapsed after its fall.
Given Benghazi’s “cradle of the revolution” status, the US believed it needed to maintain a mission there to keep up with local politics and key members of the revolution it had supported.