Emerging from the 1980 census is the picture of a nation developing more and more regional competition, as population growth in the Northeast and Midwest reaches a near standstill. This development -- and its strong implications for US politics and economy in years ahead -- has enthroned the South as America's most densely populated region for the first time in the history of the nation's head counting. Altogether, the US population rose in the 1970s by 23.2 million people -- numerically the third largest growth ever recorded in a single decade. Even so, that gain adds up to only 11.4%, lowest in American annual records except for the Depression years.