The Second Anglo-Boer War had no sooner commenced with the ultimatum of the Transvaal Republic on 9 October 1899, than Mr Schreiner found himself called upon to deal with the conduct of Cape rebels. The rebels joined the invading forces of President Steyn, whose false assurances Mr Schreiner had offered to an indignant House of Assembly only a few weeks before. The war on the part of the Republics was evidently not to be merely one of self-defence. It was one of aggression and aggrandisement. Mr Schreiner ultimately addressed, as prime minister, a sharp remonstrance to President Steyn for allowing his burghers to invade the colony. He also co-operated with Sir Alfred Milner, and used his influence to restrain the Bond.