On this date in 1402, the second Ming emperor Zhu Yunwen (朱允炆 b. 1377) died in a palace fire. Reigning as the Jianwen Emperor (建文 r. 1399-1402), Yunwen as the grandson of Ming founder Zhu Yuanzhang (朱元璋 r. 1368-1398). After taking the throne, Zhu Yuanzhang enacted a series of reforms/edicts, one of which was to mandate the imperial line of succession be the first son of the emperor. (One suspects Yuanzhang just wanted to avoid a terrible headache–the man had 24 sons after all.)
Zhu Yuanzhang’s first son, Zhu Biao 朱標, predeceased his father, and so according to the code, Zhu Biao’s first son became the new crown prince, by-passing his 23 uncles. Not good.
One of those uncles, Zhu Di 朱棣, was a talented commander and a cunning strategist. Perhaps a bit too cunning. Zhu Di had been dispatched north to the area around the old Yuan Dynasty capital of Dadu (present day Beijing) to keep an eye on the Mongols, who were still spoiling for a fight.
Zhu Di was already unhappy and Yunwen, upon taking the throne, poured gasoline on the fire by taking a series of steps to limit the powers of the regional commanders, especially