At the crux of American history stands the nation’s Civil War. Four strenuous years of blood-letting forced recalcitrant state sovereignties to recognise the permanence of the Union and the primacy of its federal authority. The emancipation of four million black slaves, though not part of the war’s formal agenda at the outset, became a means, and eventually an end, of the North’s victory on the battlefield; African-Americans’ freedom set in train an evolution of race and labour relations that continues to this day. The world’s first mass democracy demonstrated that popular, elective government, then in its infancy, need not be a casualty of war. Abroad, too, the war helped inspire nationalists, liberals and progressives: many flocked to the Union’s colours, even as conservatives rejoiced at the prospect of the failure of the Yankee experiment in republicanism.