While the introduction of wheat into early full-scale farming systems of northern China has received much research attention over the past two decades, few studies have looked at when and how the cultivation of barley, which is better adapted to colder climates, spread across East Asia. New radiocarbon (14C) dates obtained from archaeological barley grains together with material evidence suggest that the crop was introduced to Primorye (Russia’s border region with China and North Korea) no later than the 2nd century BCE, although an earlier arrival sometime between the 4th and 3rd centuries BCE seems possible. From Primorye, the crop probably spread further eastward to Hokkaido. The combined archaeological and chronological evidence suggests that barley-cultivating cultural groups may have migrated to southern Primorye from areas to the west or from southern Liaoning/north-western Korea, which rules out a dispersal via the northern Eurasian steppes or the Japanese archipelago. We propose that a combination of cultural and climatic factors was the driving force behind this migration. While we identify the eastward expansion of the Warring State of Yan around 300 BCE as the primary driver that pushed barley-cultivating populations to migrate, it seems possible that long-term cooling and drying less favourable for farming during 1000–300 BCE added to the political unrest at the northern and eastern boundaries of the Chinese Warring States, or may even have amplified their policies of territorial expansion.
