Why is America so polarized?

In Italy, 3 parties that do not agree on everything make up the gov't- The People of Freedom, Lega Nord, and The Movement for Autonomies. Lega Nord has communists and Christian Democrats in it, People of Freedom is like a Republican party, and Movement for Autonomies is a Centrist and regional party. In America there are Republicans who will never say that Kennedy, or Johnson did good things. And Democrats who think that Reagan and Nixon didnt do ****. No one can deny history. If people want to say, "Its Johnson's fault for Vietnam, and we never should have been there" then you better also think that we had no purpose being in WWI, Korea, or the Mexican-American War. Also, those Republicans who think he was corrupt and shouldn't have won, neither should Rutherford Hayes, yet we never talk about his corrupt bargain. People who say that Reagan was a false illusion, you cannot deny that he was crucial in ending Communism in Russia and propelling our economy forward, its a proven fact that while in office the economy went up. Why is it that in multi-party Democracies people can get along and look at the other side, and here where it is just 2 parties party loyalists act like s and dont look at history, not just numbers. Yeah employment went up under FDR, but more importantly he helped beat Hitler, and no numbers are needed to see the good he did. So, yes America is the land of freedom, but without more than two voices it seems like all that happens is that one side makes some good changes and some bad, and the other rolls back both the good and the bad (most of the time) and put in their own agenda. Is there ever going to be any progress?