I guess you missed the 50's and 60's a few decades back.
What was different in the 50's and 60's? America in that era still had a unifying principle accepted by the majority of the residents of the United States. The unifying principle was based on acceptance of a shared culture and creed. Since that era America has become multicultural. Multiculturalism is the antithesis of unity. Look at multicultural societies. Are any of them unified? Is Canada unified? In this era shared culture doesn't exist in America, and therefore culture is not a unifying principle.
That leaves creed. In the last half century the ideal of individual liberty has been weakened as the Left captured institution after institution. The idea of equality before the law as a component of individual liberty has been replaced by equality of outcome in much of the country. However, individual liberty and equality of outcome are ideas which do not intersect. Thus, creed is being undone as a unifying principle. During the Depression things were desperate and dire for most Americans, but they still had a common culture, and the basics of a shared creed.
The Left is relentless in its crusade to transform America from what it was into something new and different. Barack Obama is the physical incarnation of that crusade. This crusade is increasingly opposed by the old traditional America that still subscribes to the idea of America as it was founded. Leftist relentlessness is opposed by an increasingly strong counter-revolution. That is why America is more divided today than at any time since the Civil War.