Well, exactly - that explains a lot of the current political/cultural fragmentation of the U.S. population. Although you can definitely argue that though it is a "short" story in comparison, the founding of the U.S. as a revolution to gain independence from the British Crown to found a state by the people, for the people, with its own constitution and Bill of Rights is a "big" story nonetheless.
As to your other questions - good questions - one could write a whole book (or several) addressing them.