When the Nationalists routed a ragtag Red Army on the Xiang River during the Long March, an earthy Chinese peasant with a brilliant mind moved to a position of power. Eight years after his military success, Mao Tse-tung had won out over more sophisticated rivals to become party chairman, his title for life. Isolated by his eminence, he lived like a feudal emperor for much of his reign after blood purge and agricultural failures took more lives than...