To bring in territory into an existing unit (such as a country, state, county, or city).

annex

The definition of annex means to attach something, particularly to a larger entity. An example of annex is to acquire new states into a country. To incorporate into a country, state, etc. the territory of (another country, state, etc.)

Explanation:

i believe that the answer to the question provided above is that  establishing smaller ethnic communities within larger communities  gives more chance for people to know each other more but this might lead to the  conflict between groups.

"a government in which power is divided between state and national levels". federalism is a system of government in which entities such and state and province, share power with the national government.