You guys are all right but also all wrong about China's history.
China has always been like 5-6 divided people/ethnicities in different regions with different cultural customs and languages fighting over territory. The Han is the biggest majority but even that identity didn't really become a serious ethnic marker until around maybe the Ming dynasty. Before then it was mostly about family and social affiliation which formed massive city states and then were in turn married into kingdoms. Sometimes those kingdoms got so large they turned into dynasties.
Japan or the various shogunates/daimyos that made up Japan back in the early medieval era (by the european timeline) were very much patterned off of the Tang dynasty. Japan didn't really start to form its own unified identity until around the 16th century which precipitated the Imjin wars. This is when various Japan shogunates unified to invade to take Korea as a vassal. It was a way to bridge the authority between Japan and the ruling and regionally dominant Ming dynasty of China at the time. Since the 16th century it's nearly undeniable that Japan has had designs on the entire region. It's historically a fairly recent development but still pretty old and it explains a lot of the imperialist ambitions of Japan in WW2 too. It's Japan's manifest destiny.
Prior to the 16th century the only "Chinese" dynasty to ever try and conquer the islands where Japan was based were the Yuan Dynasty which were the Mongols. The Yuan dynasty were an extension of Kublai Khan (and Genghis Khan) and his empire. They were not Chinese to begin with.
China has always been like 5-6 divided people/ethnicities in different regions with different cultural customs and languages fighting over territory. The Han is the biggest majority but even that identity didn't really become a serious ethnic marker until around maybe the Ming dynasty. Before then it was mostly about family and social affiliation which formed massive city states and then were in turn married into kingdoms. Sometimes those kingdoms got so large they turned into dynasties.
Japan or the various shogunates/daimyos that made up Japan back in the early medieval era (by the european timeline) were very much patterned off of the Tang dynasty. Japan didn't really start to form its own unified identity until around the 16th century which precipitated the Imjin wars. This is when various Japan shogunates unified to invade to take Korea as a vassal. It was a way to bridge the authority between Japan and the ruling and regionally dominant Ming dynasty of China at the time. Since the 16th century it's nearly undeniable that Japan has had designs on the entire region. It's historically a fairly recent development but still pretty old and it explains a lot of the imperialist ambitions of Japan in WW2 too. It's Japan's manifest destiny.
Prior to the 16th century the only "Chinese" dynasty to ever try and conquer the islands where Japan was based were the Yuan Dynasty which were the Mongols. The Yuan dynasty were an extension of Kublai Khan (and Genghis Khan) and his empire. They were not Chinese to begin with.