Conquest and discovery has been an important part of developing the global political structure of today's Earth. After we expand and settle other planets, whether within the same solar system or not, eventually the colonies will grow and develop to the extent where they feel able to self-govern. Given that extraterrestrial colonies and their resources would be incredibly valuable to their parent government, they would be naturally hesitant to let them go, whether because of fear of a lack of control or fear that the new government will be forcibly assumed by a competing terrestrial government.
Easily, historical examples can be found by looking at overseas colonies - except for two incongruities: firstly, the process of setting up not only a self-sufficient extraterrestrial colony, but a self-expanding extraterrestrial colony would require much more assistance than, say, setting up a self-expanding overseas colony. Additionally, the area available for a colony to expand into is much greater than historically: there's a whole planet out there! Would the self-governing colonies, after they finally stabilize, cover much greater area than their parent nations? Would it be continental, global, or even include the local moon(s)? Would they be powerful enough to peacefully hold this territory, or would competing, established governments/colonies be conterminously fighting for greater resources?
How would the situation differ were the planet found inhabitable as opposed to requiring a (possibly international) terraforming project?
In short, what type of interplanetary political structure would be most likely to develop, and what historical parallels are there to support your claims?