Although America has a history of taking a commercial approach to international relations, purchases are rarely made without controversy. When Thomas Jefferson bought Louisiana in 1803, doubling the size of the country, he had to set aside his zest for constitutional constructivism, which would have ruled out such bold federal action. Sixty-four years later, when William Seward, then secretary of state, purchased Alaska from Russia for $7.2m ($162m today), the move was dubbed “Seward’s folly”. Today the Alaska deal is seen as a masterstroke and the Louisiana purchase the greatest achievement of one of America’s greatest presidents. In hindsight, both look extraordinarily good value.