In the mid-nineteenth century, China experienced a conjunction of internal crisis and external calamity that permanently weakened the Qing dynasty, thus guaranteeing the Sinosphere's eventual destruction. From the First Opium War onwards, the Manchu Raj confronted a barbarian menace on its maritime frontier that directly threatened its economic heartland, and could be subdued neither through the force of arms nor through the munificence of imperial largesse. Confounding historical precedents, whereby pastoral conquerors from the steppe had been progressively Sinicised and thus ‘civilised’ into conformity with the Sinosphere's norms, the seaborne barbarians of the British East India Company proved incapable of instruction or assimilation. Worse still, the British carried with them heretical beliefs that soon found purchase among south-eastern China's alienated peasantry, fuelling a wave of rebellions that came within an ace of toppling the imperial household. From a population of approximately 410 million in 1850, China's population is estimated to have fallen to approximately 350 million by the time the last of the mid-century rebellions was suppressed in 1873.