Complex sentence: Mesih's support within the government allowed him to weather the deposition and execution of Gedik Ahmed on 18 November 1482 and soon advanced to second vizier within the "divan" when Davud Pasha, hitherto second vizier, acceded to the Grand Vizierate in summer 1483.
Split into simpler sentences: Mesih's support within the government allowed him to weather the deposition and execution of Gedik Ahmed on 18 November 1482. He soon advanced to second vizier within the "divan" when the previous incumbent, Davud Pasha, acceded to the Grand Vizierate in summer 1483.