South African Republic and the Orange Free State issued a joint ultimatum to the British government to retract their demands. The British government did not give in to the ultimatum, and two days later, on 11 October 1899, the Second Anglo-Boer War (South African War) broke out. When the British army marched on Pretoria in May 1900, the government was forced to flee the capital. From that moment on, Reitz was responsible for the continuous relocation of its seat throughout the Transvaal, which occurred sixty-two times until March 1902. In May of that year, Reitz took an active part in the peace negotiations with the British, and he was one of the signatories of the Treaty of Vereeniging, signed in Pretoria on 31 May 1902. Self-chosen exile and return to politics Although instrumental in drafting the Treaty of Vereeniging, Reitz personally did not want to swear allegiance to the British government and chose to go into exile. On 4 July 1902, he left South Africa and joined his wife and children in the Netherlands. To alleviate his financial troubles, Reitz set out on a lecture tour in the United States. A waning interest in the Boer cause since the war was over made the tour fail and forced Reitz to return to the Netherlands. There, his health failed him again, leading to his hospitalisation and an extensive period of convalescing. He was then supported by his friends W.J. Leyds and H.P.N. Muller and the Nederlandsch Zuid-Afrikaansche Vereeniging (Dutch South-African Society). In 1907, after the old Boer republics received self-government, and in the run-up to the formation of the Union of South Africa, leading Afrikaner politicians J.C. Smuts and L. Botha asked Reitz to return to South Africa and play a role in politics again. Together with his wife, he established himself in Sea Point, Cape Town. In 1910, already sixty-six years old, he was appointed president of the Senate of the newly formed Union of South Africa. These were no easy years, again, as former Afrikaner compatriots found each other on two sides of the political fence, in a rapidly changing world. As in his earlier life, Reitz remained a man of outspoken convictions, which he aired freely. As such, he came into conflict with the Smuts government, and in 1920 he was not re-appointed as president of the Senate. He did remain a member of that House until 1929,