John Whitman’s paper brings together linguistic and archaeological evidence for the spread of agriculture in Korea and Japan. The image (left) is from Whitman, and summarizes the archaeological picture. He makes a good case that this fits with known linguistic and epigraphic evidence.
Whitman, Northeast Asian Linguistic Ecology and the Advent of Rice Agriculture in Korea and Japan John December 2011, Volume 4, Issue 3-4, pp 149-158 14 Jan 2012 Preview here.
The languages of Northeast Asia show evidence of dispersal from south to north, consistent with the hypothesis that agriculture spread north and east from the vicinity of Liaoning, beginning with the millets approximately 5500 BP. Wet rice agriculture in Korea and Japan results from a later spread, also beginning in Shandong, crossing via the Liaodong peninsula and reaching the Korean peninsula around 1500 BCE. This dispersal is associated with the Mumun archaeological culture after 1500 BCE in the Korean peninsula and the Yayoi culture after 950 BCE in the Japanese archipelago. From a linguistic standpoint, it is associated with the entry of the Japonic language family, first into the Korean peninsula, subsequently into the Japanese archipelago. The arrival of Koreanic is associated with the advent of the Korean-style bronze dagger culture and a temporary hiatus in wet rice agriculture sites around 300 BCE. Both Koreanic and Japonic are relatively shallow language families, with Koreanic the shallower of the two, consistent with the chronology above. The gap between the earliest linguistically motivated dates for these language families and the archaeological events is the result of a linguistic founders effect, providing further evidence for demic diffusion as a source for their distribution.