From Diamonds, Gold, and War: The British, the Boers, and the Making of South Africa, by Martin Meredith (PublicAffairs, 2008), Kindle pp. 433-435:
Stung by accusations that the war had been mismanaged, the British government ordered a change of command and appointed as commander-in-chief Field Marshal Frederick Roberts - ‘Lord Bobs’ - a diminutive, 67-year-old war hero, blind in one eye; but it was decided to leave Buller in charge of the Natal army. Two more divisions - the last readily available - were despatched from England. The government also realised that it had been trying to fight the wrong kind of war, relying too much on slow-moving infantry battalions to deal with mounted Boer riflemen using highly mobile tactics; British mobility needed to match Boer mobility. Britain called for civilian volunteers to join a new ‘Imperial Yeomanry’. Some 20,000 men from the ‘hunting and shooting’ fraternity signed up, including thirty-four members of parliament and peers. The City of London paid for one thousand volunteers. Further reinforcements came from other parts of the empire - from Canada, Australia and New Zealand. By January 1900, the total number of troops Britain had shipped to South Africa had reached 110,000. Additional support was provided by uitlander refugees and colonial volunteers formed into two mounted corps of their own - the Imperial Light Horse and the South African Light Horse - financed in part by Wernher, Beit & Co.
Even members of the Indian community in Natal - originally immigrants employed as indentured labourers to work on sugar plantations - volunteered to serve as stretcher-bearers. Their organiser was a 28-year-old lawyer, Mohandas Gandhi, who had arrived from India in 1893, spending a year in Pretoria before settling in Durban. Gandhi expressed sympathy for the Boer cause but considered he was bound by loyalty to Britain. ‘I felt that, if I demanded rights as a British citizen, it was also my duty, as such, to participate in the defence of the British Empire.’ The Natal authorities at first turned down Gandhi’s offer. But after Black Week, their attitude changed. Gandhi’s ambulance corps of ‘free’ Indians and indentured labourers recruited 1,100 volunteers.
Just as the British won support from the empire, so Boer ranks were bolstered by foreign volunteers. Some 2,000 uitlanders - Germans, French, Dutch, Irish, Irish-Americans, Russians, Scandinavians, even some English - joined the Boer cause. Another 2,000 foreign volunteers arrived from abroad. A retired French army colonel, Count de Villebois-Mareuil, enlisted, hoping to capture Cecil Rhodes. ‘History will add a fresh flower to the glory of France,’ he wrote in his diary. ‘To take Kimberley and see the face of the Napoleon of the Cape.’ He rose to the rank of Vecht-generaal - combat general - but was killed in action in April 1900. In all, the Boer allies were able to raise armed forces totalling more than 70,000 men. In addition, about 10,000 Africans served as auxiliaries to Boer commandos - retainers, porters, gun-bearers and labourers - many of them conscripted under duress.
Yet early Boer advantages were soon frittered away by poor strategy. By committing such a large proportion of their forces to the siege of three towns, Boer generals lost the opportunity to drive deeper into Natal and the Cape Colony when both areas were highly vulnerable to mobile attack. As their forward thrusts began to ebb, they turned to a more defensive stance, preparing for a much tougher British assault. By December, the Boer offensive had reached its limits. Unlike 1881, there had been no crushing blow to induce the British to negotiate.