Enslaved or free? As Kris Manjapra relates in this history of slavery and emancipation in the 19th century, the question was never quite as simple as it appears. In Manjapra’s telling, slavery was ‘a centuries-long war against African peoples’ and the various emancipations that occurred in the United States, the Caribbean and Africa were not the glistening triumphs of humanitarianism but imperfect and compromised developments which ‘only extended the war forward in time’. These histories – and the stories of the once-enslaved – inhabit what he calls ‘the void’, a liminal place beyond the ‘ghost line’ of human memory.

Black Ghost of Empire assesses five distinct forms of emancipation that materialised during the long 19th century. The first was ‘gradual emancipation’: the practice among the northern states of the American union, beginning with Pennsylvania in 1780, of legislating that enslavement within their borders should eventually cease. It is an important story for British readers, not least because it gives the lie to the old myth that the British Empire was ‘first’ to abolish slavery. Yet, as Manjapra relates, gradual emancipation was a convoluted and often cruel process: some state laws which granted freedom to newborn children did not emancipate their parents; others prescribed liberty only when a person reached a given age. In 1777, for instance, the republic (later the state) of Vermont awarded freedom to all men over the age of twenty-one and all women over nineteen, but children remained in slavery there until 1810.

The other great emancipation in the United States was, of course, what Manjapra calls ‘war emancipation’, though, perhaps surprisingly, he has little time for the idea that slavery was the root cause of the American Civil War. He provides a compelling account of Reconstruction and the introduction of