It means that our country will be as different after the coming upheaval from what it is now as it was before and after the upheavals of 1776, 1860, and 1943.
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1943??
Actually the whole period from about 1930 to 1945. I can't think of any single event (year) in the Depression or WWII that represents the principle turning point so my choice of 1943 was kind of arbitrary.