WordNet sense 1 (a particular environment or walk of life):

area, arena, field, orbit, sphere

WordNet sense 2 (territory over which rule or control is exercised):

demesne, land

WordNet sense 3 (people in general; especially a distinctive group of people with some shared interest):

world

WordNet sense 4 (a knowledge domain that you are interested in or are communicating about):

realm, region