I was at the local library leafing through the beginning of Autumn in the Heavenly Kingdom by Stephen Platt. In it he makes two explosive claims: 1. Western intervention, and by far above all British aid, was decisive in the Qing victory, and 2. The American Civil War coincided with the decisive turning points of the Taiping war. Britain would not have been able to ramp up its efforts in the east had it interfered in the US, and the Taiping could have emerged victorious.
What if the UK intervenes in the civil war in 1861/62? What attention or resources that went to aid Qing China against the Taiping state would have went to North America instead, and how would it have affected the outcome of that war?