Distilleries have been in America for quite some time now. With a few starting in the 1700s but most starting up from the beginning of the 1800s. There was such a boom in distilled liquor that the church took action warranting its first regional abstention against alcohol in the regions of New York and Maine in 1808 and 1826, respectively. These distilleries grew in number around the country to a rapid decline in around the time of Prohibition, whose effects lasted until the 1950s.
The majority of American Whiskey, though by no means all, is made in the state of Kentucky. This is the home to illustrious Bourbon Whiskeys that almost all around the world have heard of. The most famous brand that gets tossed around the place is Jim Beam (though legally not a Bourbon Whiskey due to being bottled at under 40%abv) alongside of the incredibly decent Jack Daniels. Where Scotch and Irish Whiskys are made from rye or barley, Bourbon is famously made with corn as its base. This is not because the Americans chose to be different, or difficult, to British tradition but rather out of respect to the native American Indians. Kentucky became the home to Bourbon Whiskey in the late 1750s and was initially made from imported barley or rye though it was in the late 1770s when the Governor of Virginia offered up 400 acres of 'free' land to the natives. The native Indians chose to grow their local corn across the state now known as Kentucky. Over time rye and barley have been used to supplement the Whiskeys as well as giving the final products a slightly more fuller aromatic presence and texture.
Many are familiar with Bourbon Whiskey but there is a raft of blended American Whiskey made each and every year. An American blended Whiskey is one that is made from at least two straight Bourbons and/or a rye Whiskey. A straight Bourbon is one that has been made from one distillery. Then a blended Bourbon is one that contains at least 51% of a single straight Bourbon and then a raft of other straight Bourbons to make up the rest of the blend.