The USA is not a democracy, it is a constitutional republic. The architects of the system were highly suspicious of Athenian democracy and the tyranny of the majority.

Third parties don't really work in this system. If a third party gains transaction on an issue, one of the two main parties will largely adopt those policies. Otherwise, the 3rd party just splits the vote and the party least like the third party wins.

Everything is always changing too. Both parties have changed quite a lot in even the last 10 years.

Even further back look at an election map of JFK and Nixon in 1960. The states have practically all flipped. California and the west coast voted all Republican. The southern states voted all Democrat.