I went to see the historian Simon Schama at his Columbia University digs, where I found him tormented by the research for his new book, Rough Crossings. It explores the role of slavery when America wrote down its "idea" and declared independence in 1776.

Schama found that the gentry - Washington, Jefferson et al - had actually taken up arms because the Brits offered freedom to slaves joining the Loyalists. "I don't want to start a fight, I'm a peaceful man, but the War for Freedom turns out to have been a War for Slavery!" he sputtered.

It was also a war for rum, not the tea famously dumped in Boston harbour. Ian Williams, the author of Rum, A History of the Real Spirit of 1776, says that if today's wars are all about oil, New Englanders of old fought over sugar, which they used to distil rum. But, rather than buy British Caribbean sugar, they saved a packet by trading with the French, then at war with King George.

"The colonists made low-grade rum, but even used it to buy slaves," says Williams. "What would teetotal Bush, the freedom crusader, make of this?"