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(Yemaek) along the middle reaches of the Yalu, Imdun in the Hamh ŭ ng plain on the northeast seacoast of the Korean peninsula, and Chinb ŏ n in today’s Hwanghae province in North Korea. Chin emerged in the region south of the Han River around 430 BC , and at about the same time some people of Chin found their way into western Japan.
    Among these walled-town states the most advanced was Old Chos ŏ n, established before the eighth century BC at the latest. Originally Old Chos ŏ n appears to have been just a small political entity dominating a minor portion of the Liao River plains, but by the early fourth century BC it had entered the Iron Age and proceeded to incorporate, by alliance or military conquest, other walled-town states scattered throughout the vast region between the Liao and the Taedong rivers to form a large confederation. At this stage Old Chos ŏ n was entitled to be called a confederated kingdom.
    Old Chos ŏ n held its court at Pyongyang. At the time there were three different sites called “Pyongyang” (meaning “flatland”): one west of the Liao River, a second east of the river, and the third in northwestern Korea. One can surmise that the first capital of Old Chos ŏ n was located west of the Liao River, was then transferred east of the river as the Chinese forced Old Chos ŏ n out of the region, and finally, with the decline of its power, was relocated in present-day Pyongyang in its last years.
    By the late fourth century BC the northern Chinese state of Yan had begun to use the term
wang,
or king, upon the decline of the suzerain Zhou kingdom. Old Chos ŏ n assumed the same title for its ruler and firmly maintained equal relations with China’s regional lords in the Warring States Period (403–221 BC ). In about 320 BC , when Yan attempted to invade its territory, Old Chos ŏ n planned a counterattack. As the two states confronted each other, Old Chos ŏ n’s commanding posture caused the Yan people to criticize the Korean nation as “arrogant and cruel.” There is no doubt, in short, that Old Chos ŏ n exhibited formidable strength at that time as an independent power in Northeast Asia.
The Coming of the Iron Age
    During the Old Chos ŏ n period the Bronze Age was fated to pass. In the early fourth century BC commodities fashioned from iron began to enter southernManchuria and the Korean peninsula from China, and by 300 BC iron implements had widely come into use.
    Iron culture was first introduced to southern Manchuria and northwestern Korea, Old Chos ŏ n’s territory, and from there it soon spread in all directions. At the same time another Bronze culture of Scytho-Siberian origin took root in Manchuria and the Korean peninsula. As iron implements came into use, the mode of life in Korea underwent profound changes. First of all, with the use of hoeing implements made of iron and sophisticated iron farming tools such as plowshares and sickles, agriculture experienced remarkable development. Food production markedly increased compared to that of the Bronze Age. The increased output, however, was not shared equally by the whole society but was monopolized by a ruling class. Thus the rulers wielded even greater authority than before.
    Iron culture also influenced weaponry. Iron weapons such as daggers and spear points as well as bronze daggers, spear points, and spears have been excavated from Iron Age remains in large numbers. These sharp weapons fashioned from hard metal were monopolized by a small number among the ruling elite. Members of the ruling class also mounted on horseback or rode horse-drawn vehicles in imposing their authority on the rest of the people. These horse-riding warriors were the undisputed masters of Iron Age society.
    People in the Iron Age who lived in pit dwellings or huts began to use
ondol,
the traditional Korean underground heating device in which the stone that constituted the room floor was heated by hot air circulating beneath it. This unique heating