If the US has a national spirit, it would have to be Bourbon - by definition, a spirit distilled from a mash that's at least 51% corn to less than 80% ABV and aged in new charred oak barrels. The flavours imparted by the new American oak tend towards vanilla, clove and caramel. Varying proportions of different grains in the mash make for different styles. Wheat and rye are common; the latter adding spice and complexity. However a little goes a long way - as little as 5% can make a significant impact.