David George Ritchie, who is known as one of the leading philosophers of British Idealism, has been considered as one of key figures of the New Liberalism by some scholars. While highly praising Kant's theory of perpetual peace, he took sides with the British Empire in the Boer war. His case for the British war policy drew condemnation from the New Liberals, such as J. A. Hobson and J. M. Robertson. The purpose of this inquiry is to make plain the reason why Ritchie championed Britain's cause of the war, and to clarify the differences of view among the New Liberals about the war and the the empire. Whereas Hobson regarded capitalism as a driving force of the war, and asserted that the British Government was engaged in an unjust war, Ritchie maintained that the British war policy was justified by the ethical judgment that every war should be discussed on its causes, ideals and purposes. According to him, the British Empire, which represented a higher stage of human society, was preparing the way for a federation of the world, which would absorb smaller nations into larger political bodies and prevent war within great areas.