Multinational states most often have political problems because

Hello there!

Your answer would be each nation desires an independent sovereign state.

The reason why "each nation desires an independent sovereign state" is because Multinational states are not really known to handle having an economy without having any political problems. People that are part of Multinational states would want to have their own state, due to the  fact that the person that is leading them is not the same ethnic group as them, and this causes separation in the state. These kind of states most likely has had a movement called the "separatist movement." They made these movements because they wanted to be independent form the government that is controlling the land. To sum it all up, different ethnic groups don't really work together when it comes to a political stand point.