On 28 May 1900, Lord Roberts issued a proclamation (back-dated to 24 May 1900) stating that the Orange Free State (OFS) Boer republic was annexed as the Orange River Colony (ORC). This article deals with the British allegations that they had conquered the OFS, as early as the end of May 1900. It deals especially with the legality of these averments in the context of the law of nations. The opinions of a number of legal authorities are evaluated and applied to the situation prevailing in the OFS. Several other proclamations and opinions are also taken into consideration, as well as the events in the Brandwater Basin in July and August 1900, when a very significant number of the OFS forces in the field surrendered. The positions of and comments by General CR de Wet and President MT Steyn are evaluated, and the decisions handed down in a number of post-war court cases are considered. New light is shed on the legal status of the Boer representatives taking part in the negotiations leading up to the signing of the Peace of Vereeniging on 31 May 1902.