The date of origin of kimchee is unknown, but salt fermented vegetables were fairly commonplace by 500 CE, and the process well established. Korean radish was the most common vegetable used.

Chili peppers did not appear in kimchee until 1614 and their use was not widespread until the 19th century, when it was discovered that sufficient chili reduced the amount of expensive salt needed. There is no evidence Napa Cabbage (actually a turnip green) was brought to Korea before the late 19th century. Lists of kimchee ingredients are extant from much earlier time into the 19th century, but no form of cabbage (real cabbage or turnip greens) is mentioned.

I read an absurd Korean denial of all this claiming that cabbage kimchee with chilis was made "thousands of years ago", which is impossible, because all chilis originated in South and Central America, and were brought to East Asia by the Portuguese around 1600. Some researchers think birds may have carried one variety of chili to Africa before arrival of the Portuguese, but this is doubtful.

Certainly there were none in East Asia until the Portuguese brought them. One of the hottest species is called chinense, but that was a mistake by a botanist who saw so many in East Asia he thought they must have originated there. They came from Brazil.