By 1368, Han Chinese forces had driven the Mongols out of China. The first of the new Ming dynasty's emperors, the Hongwu Emperor, and his son, the Yongle Emperor, produced tributary states of many Central Asian countries. The suzerain-vassal relationship between Ming empire and Timurid existed for a long time. In 1394, Hongwu's ambassadors eventually presented Timur with a letter addressing him as a subject. He had the ambassadors Fu An, Guo Ji, and Liu Wei detained. Timur eventually planned to invade China. To this end Timur made an alliance with surviving Mongol tribes based in Mongolia and prepared all the way to Bukhara.