In 1424, Zhu Gaoxi, the Hongxi Emperor, upon ordering the cessation of the famed Ming Treasure Voyages, is killed in a fire sparked by a "Bright Dragon", now believed to have been ball lightning. His wife and all his sons die with him, alongside several prominent Confucian scholars. His untimely demise leads to his brother's adcension to the throne, as the Tienfu Emperor. Interpreting his brother's death as Heaven's intervention, he countermands the order to cease the voyages and maintains China's fleet, though the famed Treasure Ships are slowly disassembled over the next few decades. This prevents China's self-imposed isolation and leads to an expansion of her commercial sphere of influence over Southeast Asia.
This in turn leads to a very different colonization history in the Americas and Asia as Portugal races to outdo the Chinese and accelerates her naval projects. Her naval buildup means Spain's naval assets are virtually destroyed in the War of Castilian Succession, forcing Columbus to turn north to find patrons for his voyages west, which leads to England, not Spain, initiating European colonization of the New World.
Furthermore, China's greater political and military influence in East and Southeast Asia reduces the influence of Europeans in the area, therefore Japan, once united, does not undergo the sakoku policy of self-isolation and instead remains an active power on the world stage. However, due to China's greater military strength, particularly her navy, the Imjin War does not take place and Japan instead looks elsewhere to expand, including the new lands discovered by the Europeans.
China's commercial and diplomatic expansion is spearheaded by one particular person, Zheng He, the eunuch admiral that projected China's image through South East Asia, India, and as far west as the Somali coast of East Africa. While his time was short, his family would carry his torch as prominent figures in China's economic, diplomatic and military history.