When you want to build a network, such as the Internet or the national road network, you don't put in a lot of random links. Instead you have a mixture of local links forming local clusters, and long distance links between clusters. This can continue for more levels.
Now we come to the interesting observation that people divide up, corresponding roughly to the right/left divide in politics, between people who want friendship and support to extend only to their local group (or groups), and those who want to extend help and support more broadly, with some extending that to all humanity. This division is just what you need to efficiently build networks of people.
A key feature of humans is our ability to move from simple things to multi-level recursively defined things. We see that most obviously in human language compared to the simpler communications of our related species. And indeed it is notable the way that nations relate to each other in ways that seem similar to the way that humans interact.
