The main title of John Darwin’s new book is simple but mischievous. Its primary purpose is to announce that he sees empire as an activity rather than a thing. People, millions of them, made it, and remade it constantly, over long stretches of time; it was always in progress, always being finished. They built empire from a variety of motives, some commercial, some geopolitical, some religious, some vainglorious, but for most as a way of building a better life. Darwin wants to give us less a taxonomy of the British empire – what its bits consisted of – than an account of how it was built. He depicts the empire as constantly in flux. ‘Empire-building,’ he writes, ‘was always a work in progress, like a house extension in which the design, the builders and even the building materials were constantly changing.’ The secondary purpose of his title is thus a playful one. Wouldn’t we suspect that a finished empire was one already in decline, the victim of irresistible entropy – finished in both senses? Empires are restless, or they are dead. The play in the title, then, is that the British Empire is unfinished because it finished.