A number of Voortrekkers joined those trekboers already in Transorangia and began to make new homes in the rich Caledon valley, around mission stations where Sotho and Tswana communities had already settled. As the Boers built permanent homes, they began to claim land ownership.
The increasing Boer presence alarmed Moshoeshoe. In 1843 he requested the British authorities at the Cape to stop the Boers from building on land he considered to be his. The outcome of this request was the Napier Treaty signed between Moshoeshoe and Adam Kok, advised and assisted by the missionaries Eugène Casalis and John Philip on the one hand, and the Cape governor Sir George Napier on the other. This treaty recognised the jurisdiction of Moshoeshoe over his lands between the Orange and the Caledon rivers and also a strip of land west of the Caledon.
The treaty was immediately opposed by the Wesleyan missionaries and the chiefs whose communities they worked among, on the grounds that it took away some of their lands. In 1849 the British Resident in the recently proclaimed Orange River Sovereignty, between the Orange and Vaal rivers, established boundaries between areas claimed by the various communities. This resulted in Moshoeshoe losing some of his kingdom’s land. The period 1848–1854 marked the second phase of missionary activity in the kingdom, characterised by conflict between the Paris Evangelical Mission Society missionaries and the Sotho. In this conflict, Sotho traditionalists insisted on a return to traditional religion and practices and the expulsion of all whites, including the missionaries, from the kingdom.
Although the missionaries defended Sotho land rights, and Casalis was Moshoeshoe’s diplomatic agent, the Sotho were nevertheless upset by the missionary preaching against revenge and the theft of cattle. Leading the call for the return to tradition, Moshoeshoe kept his people away from the missionaries and led the revival of rituals of war and other tradional practices. In defiance against Christianity, he married even more wives. Although Moshoeshoe had remained loyal to all British governments at the Cape, the relationship deteriorated after the British persuaded Moshoeshoe to relinquish lands north of the Caledon occupied by the Tlokwa. He refused and after a cattle raid against the Tlokwa the British decided to enforce compliance from him. British forces invaded his kingdom in 1851 and then again in 1852, but the Sotho defeated the invaders and forced them to retreat.
In true diplomatic style, Moshoeshoe sued for peace even though effectively he had the upper hand. Two years later, the British and the Boers signed the Bloemfontein Convention, which gave the Boers sovereignty over what was now known as the Orange Free State. Consequently Moshoeshoe was to fend for himself.
Most problematic was the boundary dispute between the Boers and the Sotho in the Caledon River valley, and conflicting land claims of Chief Moroka and Korana chiefs. To settle these claims, bring peace into the area and identify future aggressors, the Warden Line was promulgated in 1849. This boundary was constantly revised but neither side was ever satisfied with it, and Lesotho continues to claim parts of the Free State right up to the present day. Moshoeshoe defeated the Free State quite comprehensively in 1858 (Senekal’s War) but was persuaded by his missionaries to allow Governor Sir George Grey to mediate. By the boundary determination of Aliwal North in 1858, Grey deprived the Sotho of the fruits of their victory without satisfying the Free Stater
This peace simply sowed the seeds of the next war. The Free State, now led by President Jan Brand, was far better prepared for the second round (Seqiti War of 1865) and the military balance of power shifted dramatically. The Free State was aided by Moroka’s Rolong and by the people of the Wittebergen reserve (later Herschel) in the Cape Colony, because they believed the Free Staters would help them gain access to more land.
The Sotho stood alone, barred by colonial laws from obtaining weapons. By the end of the following year, they were defeated by Boer numerical and military strength. Letsie, heir apparent to the aging Moshoeshoe, sued for peace. According to the Treaty of Thaba Bosiu signed on 26 March 1866, the size of the kingdom was greatly reduced, to what is today Lesotho. Two-thirds of Sotho arable land was lost through this treaty, while thousands of Sotho cattle and sheep were lost to the Boers following the defeat. After his people had harvested their crops, Letsie resumed the war, but again the Sotho were defeated. Again Moshoeshoe was forced to seek British protection. This time, on 26 March 1868, High Commissioner Sir Philip Wodehouse proclaimed the annexation of the land of the Sotho, named Basutoland, as a British protectorate.
In 1871 Basutoland was annexed to the Cape Colony. The Cape adopted a policy of making Basutoland pay for its own administration through taxation, and weakening the power of the chiefs. Development of the territory was of less importance to the authorities than the firm imposition of law and order. From their side the Sotho objected to the unilateral imposition of colonial policies, and to ways in which their taxes were being used. They requested some form of representation in the council of government, but the request was rejected. The escalating discontent of the Sotho was to spill over into the so-called Gun War of 1880–1881.
The acceptance of colonialism by the Sotho represented a compromise: British protection in return for a limited territorial integrity. It was a more desirable option than incorporation into the Orange Free State. That the kingdom survived in the face of white expansion, taxation, labour demands, and internal stress caused by tension between chiefs and commoners is an extraordinary achievement.