The exact origins of barbecue sauce are unclear but is believed to have come from South Carolina some time in the 17th century. It is generally a tomato and spice-based sauce; however, there are huge differences in varieties all over the US. Originally used to baste meat during cooking, barbecue sauce is also now more commonly served as a condiment similar to ketchup and brown sauce.
For a less sweet version, replace the ketchup with some onions and chopped tomatoes sweated until soft and blitzed with the rest of the ingredients.
For a spicy version, try adding chilli flakes or Tabasco, and for a smoky version, add a teaspoon of smoked paprika.