According to Guns, Germs, and Steel, what was the Mongols' political structure?
Diamond mentions two different political structures that the Mongols had. These structures changed over time. At first, the Mongols' society was a chiefdom. Later, as the Mongols were able to conquer an empire, their society turned into a state.
At the end of Chapter 13, Diamond states that the Mongols who conquered China were a chiefdom. At this time, they did have a centralized government, but it was less organized. It was not the sort of government that the Mongols later had when they had conquered China. At that point, they had a highly bureaucratized government wtih laws and judges, not a more informal system where issues of justice were decided more arbitrarily.
So, the Mongols had a chiefdom but then developed a state as they increased the size of their empire.