The worst thing that happened to the United States was the fall of the Soviet Union.
Before that, there was a clear difference in ideology, and it helped keep us united.
Capitalism vs. Communism
Freedom vs. Totalitarianism
Elected Government vs. a government everyone knew was a farce despite having "elections."
Equal Opportunity vs. Equal Outcome
Religious Freedom vs. State Imposed Atheism
Neighbors Helped Neighbors vs. Neighbors Spied on Neighbors
Sure we had our communists and socialists since the early 1900s, but they were a small minority and dismissed by pretty much everyone. Even in their heyday in the early parts of the 20th century they were never more than a few precent of the population.
People could get along, despite politics. Most just wanted what was best for the country, although how to achieve that was where opinions diverged.
Moral issues were handled mostly on the family, local, and state level (abortion was the outlier) and people pretty much didn't care how others lived because everyone kept their personal lives personal.
Sure our nation wasn't perfect, because it is composed of imperfect people, but it has been the best nation on this Earth since it was founded. Whether we can keep it going is the unanswered question.
"If you will not fight for right when you can easily win without blood shed; if you will not fight when your victory is sure and not too costly; you may come to the moment when you will have to fight with all the odds against you and only a precarious chance of survival. There may even be a worse case. You may have to fight when there is no hope of victory, because it is better to perish than to live as slaves." - Sir Winston Churchill