In antiquity, China was far from being the China we know today, neither in extent, nor in political and social organisation. To the south it did not extend beyond the Yangtze River, to the north it stopped short of the Mongolian steppe, to the north-east, only a small part of the south Manchurian plain was included, whereas in the west it merely went up to the easternmost part of what is now Kansu Province; the Szechwan plain was only included at the end of the fourth century B.C. Politically, the King of Chou was theoretically the overlord of most of this area, but in actual practice, independent rulers reigned over a congeries of larger and smaller states. As a result of wars of conquest, seven large states had come to be formed by the middle of the fifth century B.C. and these were engaged in a ceaseless struggle for supremacy. The time between the middle of the fifth century and 221 B.C., when the western state of Ch'in finally conquered all its rivals, is known as the period of the Warring States.