The rebel leaders of 1914 purged opponents and imposed their will by force. This new radicalism had three dimensions: personnel, policy, and practice. ‘The Revolution in power’ describes the two crucial and related issues that now occupied the political agenda: could the victorious rebels—Villa, Zapata, Carranza, and Obregón—agree, first, on a common programme and, second, on a common government which would enact it? The final big bout of civil war ran from 1914 to 1915 with the winner being Carranza due to the superior generalship of the supporting Obregón and the Carrancista. The challenges and responses of the Carranza government and the 1917 Constitution are also described.