Steve's question points up the implicit relevance of scale, or boundaries, for the definition of political systems. I'm accustomed to defining anarchy, when asked, as a social/political arrangement where no one entity has decisive power over all others. On this construction, Somalia is anarchic because the three clans rival each other in power. The structure within clans might be quite totalitarian, just as many families in the U.S. are. The degree of oppression within smaller units isn't crucial so long as there is freedom of movement between them. Currently children in the U.S. aren't allowed to choose their place of residence (as they should be able to), and clan membership is also presumably given by birth. But I think it's still meaningful to speak of Somalia, or the world, as anarchic.