Geostrategy, a subfield of geopolitics, is a type of foreign policy guided principally by geographical factors as they inform, constrain, or affect political and military planning. As with all strategies, geostrategy is concerned with matching means to ends—in this case, a country's resources (whether they are limited or extensive) with its geopolitical objectives (which can be local, regional, or global). Strategy is as intertwined with geography as geography is with nationhood, or as Gray and Sloan state it, "[geography is] the mother of strategy."