As a commentary on Mr. Cobden's assertion that the natives were being driven out of Sarawak, the population of the raj in 1850 had increased to 50,000 from 8000 in 1840, and this increase was due to immigration from the neighbouring countries, where the people had been the constant prey of pirates, head-hunters, and their own oppressive rulers, and for these over-burdened people the Rajah had supplied a haven. The Chinese colony in upper Sarawak was augmented by the arrival of five thousand Chinese refugees from Pemangkat in Dutch territory, who had come to Sarawak to escape the tyranny of their more powerful neighbours and rivals, the Chinese of Montrado. These latter had successfully rebelled against the authority of the Dutch, and were now oppressing their weaker neighbours, both Chinese and Dayak. The Kayan and Kenyahs of the Baram, who had been in rebellion against the Sultan, had sent messages offering to accept the Rajah as their chief, and those of the Rejang assisted in building the new fort at the mouth of the Kanowit. This fort was erected by the Rajah to protect the inhabitants of the Rejang delta, and of Oya and Muka, by blocking the egress by the Kanowit river to the Sekrang and Saribas Dayaks. All these countries, including the Sekrang, where a station had already been established, were under the _de jure_ rule of the Sultan, but the inhabitants now looked upon the Rajah as their ruler. The Sultan had long been helpless to govern the disturbed districts; his authority was not recognised by the population, and the chiefs appointed by him acted to gain their own ends, the enriching of themselves at the expense of the people. The Sultan had placed himself in the Rajah's hands, and was well pleased that he should pacify and introduce order into these districts, more perhaps in his own interests than in those of his own people, for whose welfare he cared little; they paid him no revenue, and that he hoped the Rajah would secure for him. Bandar Kasim, in spite of warnings, was again oppressing his people in the Sadong. The Rajah had deposed him in 1848, and had appointed his brother, Abang Leman,[176] in his place, but the change brought no benefit to the people, it gave them but an additional tyrant, for both were now behaving badly, and the Bandar had to be removed. After visiting Labuan, the Rajah went to Penang for a much-needed change, and there received instructions from the Foreign Office to proceed to Siam on a diplomatic mission. He left for Bangkok in August. To quote his own words: "The mission was a dead failure, as the Siamese are as hostile and opposed to Europeans as any people can well be. I had a very trying time of it, and altogether got rid of an unpleasant and critical position without loss of national and individual credit." A short time before an American mission had also been similarly repulsed.