Complex sentence: Overcome with grief, the Jingtai Emperor fell ill and Zhengtong decided to depose Jingtai by a palace coup which eventually reinstalled Zhu Qizhen as emperor, who named his second reign Tianshun ("heavenly obedience") and went on to rule for another seven years.
Split into simpler sentences: Overcome with grief, the Jingtai Emperor fell ill and the former Zhengtong Emperor decided to depose his brother by a palace coup. The former Zhengtong Emperor was successful in seizing the throne from the Jingtai Emperor, after which he changed his regnal name to "Tianshun" (lit. "obedience to Heaven") and went on to rule for another seven years.