The concept of an O&O is clearly defined in the United States and Canada (and to some extent, several other countries such as the United Kingdom, Australia, Brazil, Argentina, Chile and Japan), where network-owned stations had historically been the exception rather than the rule. In such places, broadcasting licenses are generally issued on a local (rather than national) basis, and there is (or was) some sort of regulatory mechanism in place to prevent any company (including a broadcasting network) from owning stations in every market in the country. In other parts of the world, many television networks were given national broadcasting licenses at launch; as such, they have traditionally been mostly (or entirely) composed of owned-and-operated stations, rendering a separate notion for such a concept redundant.