Astate is a
a. people group that share a common history, culture, and belief system
b. sovereign territory with an autonomous government
c. political unit ruled by a monarch
d. multiethnic empire, united by nationalism

The correct answer is : b. sovereign territory with an autonomous government

It does not have to be ruled by a monarch ( so answer c is not correct) and it does not have to me an empire ( so not d either).

It's also not a group of people ( so not a): it's a group of people with a territory and organization - as described in option b!