Shu Han's difficulty was that its population was not large enough to be able to stand against the northern State of Wei; moreover, it was difficult to carry out an offensive from Shu Han, though the country could defend itself well. The first attempt to find a remedy was a campaign against the native tribes of the present Yünnan. The purpose of this was to secure manpower for the army and also slaves for sale; for the south-west had for centuries been a main source for traffic in slaves. Finally it was hoped to gain control over the trade to India. All these things were intended to strengthen Shu Han internally, but in spite of certain military successes they produced no practical result, as the Chinese were unable in the long run to endure the climate or to hold out against the guerrilla tactics of the natives. Shu Han tried to buy the assistance of the Tibetans and with their aid to carry out a decisive attack on Wei, whose dynastic legitimacy was not recognized by Shu Han. The ruler of Shu Han claimed to be a member of the imperial family of the deposed Han dynasty, and therefore to be the rightful, legitimate ruler over China. His descent, however, was a little doubtful, and in any case it depended on a link far back in the past. Against this the Wei of the north declared that the last ruler of the Han dynasty had handed over to them with all due form the seals of the state and therewith the imperial prerogative. The controversy was of no great practical importance, but it played a big part in the Chinese Confucianist school until the twelfth century, and contributed largely to a revision of the old conceptions of legitimacy. The political plans of Shu Han were well considered and far-seeing. They were evolved by the premier, a man from Shantung named Chu-ko Liang; for the ruler died in 226 and his successor was still a child. But Chu-ko Liang lived only for a further eight years, and after his death in 234 the decline of Shu Han began. Its political leaders no longer had a sense of what was possible. Thus Wei inflicted several defeats on Shu Han, and finally subjugated it in 263.