I. ˈhärtˌland, ˈhȧt- -ˌlaa(ə)nd, -_lənd noun
: an area of decisive importance : a pivotal or nuclear area
the entire heartland of the country, the Mississippi Basin — A.W.Baum
the German industrial heartland in the Ruhr valley — Henry Wallace
the temperate highlands which are the heartland of the republic — A.P.Whitaker
the heartland of Eastern duck and goose shooting — Newsweek
specifically : a central land area (as northern Eurasia from the Elbe to the Amur) conceived by geopoliticians to be capable of self-sufficiency as an economic and military unit, invulnerable to sea power, and therefore having strategic advantages for mastery of the world
II. noun
: the central geographical region of the United States in which mainstream or traditional values predominate