Answer:
Law of diminishing returns: refers to the tendency for productivity to decline after a certain point with the continued addition of capital and/or labor to a given resource base. World-empires could support growing populations only if overall levels of productivity could be increased.
The usual response of empire builders to these diminishing returns was to enlarge the resource base by colonizing nearby land. This colonization had immediate spatial consequences in terms of establishing dominant/subordinate spatial relationships between world-empires and colonies.
Colonization played a role in establishing hierarchies of settlements and creating improved transportation networks as well. The military underpinnings of colonization also meant that new towns and cities came to be carefully sited for strategic and defensive reasons.