The situation of the state of Wu was much less favourable than that of Shu Han, though this second southern kingdom lasted from 221 to 280. Its country consisted of marshy, water-logged plains, or mountains with narrow valleys. Here Tai peoples had long cultivated their rice, while in the mountains Yao tribes lived by hunting and by simple agriculture. Peasants immigrating from the north found that their wheat and pulse did not thrive here, and slowly they had to gain familiarity with rice cultivation. They were also compelled to give up their sheep and cattle and in their place to breed pigs and water buffaloes, as was done by the former inhabitants of the country. The lower class of the population was mainly non-Chinese; above it was an upper class of Chinese, at first relatively small, consisting of officials, soldiers, and merchants in a few towns and administrative centres. The country was poor, and its only important economic asset was the trade in metals, timber, and other southern products; soon there came also a growing overseas trade with India and the Middle East, bringing revenues to the state in so far as the goods were re-exported from Wu to the north. Wu never attempted to conquer the whole of China, but endeavoured to consolidate its own difficult territory with a view to building up a state on a firm foundation. In general, Wu played mainly a passive part in the incessant struggles between the three kingdoms, though it was active in diplomacy. The Wu kingdom entered into relations with a man who in 232 had gained control of the present South Manchuria and shortly afterwards assumed the title of king. This new ruler of "Yen", as he called his kingdom, had determined to attack the Wei dynasty, and hoped, by putting pressure on it in association with Wu, to overrun Wei from north and south. Wei answered this plan very effectively by recourse to diplomacy and it began by making Wu believe that Wu had reason to fear an attack from its western neighbour Shu Han. A mission was also dispatched from Wei to negotiate with Japan. Japan was then emerging from its stone age and introducing metals; there were countless small principalities and states, of which the state of Yamato, then ruled by a queen, was the most powerful. Yamato had certain interests in Korea, where it already ruled a small coastal strip in the east. Wei offered Yamato the prospect of gaining the whole of Korea if it would turn against the state of Yen in South Manchuria. Wu, too, had turned to Japan, but the negotiations came to nothing, since Wu, as an ally of Yen, had nothing to offer. The queen of Yamato accordingly sent a mission to Wei; she had already decided in favour of that state. Thus Wei was able to embark on war against Yen, which it annihilated in 237. This wrecked Wu's diplomatic projects, and no more was heard of any ambitious plans of the kingdom of Wu.