Thanx to
Duverger's Law, the US has been dominated by pairs of political parties over its history. But once every so often, they reorganize.
First Party System: 1796 - 1824
The creators of the US Constitution wanted no political parties, but they could not keep people from dividing themselves into factions.
Federalist Party: Alexander Hamilton
Democratic-Republican Party: Thomas Jefferson, James Madison
The Feds dominated until 1800, then the D-R's after that, with the Feds gradually dwindling to a few isolated strongholds, and then disappearing.
Second Party System: 1828 - 1854
The Democratic-Republican Party split in two.
Democratic Party: Andrew Jackson
National Republican Party, then Whig Party: Henry Clay
Third Party System: 1854 - 1896
Whig Party collapsed, Republican Party emerges.
Democratic Party: southern, associated with liturgical churches (Catholic, some Protestant)
Republican Party: northern, associated with pietistic churches (Protestant)
Fourth Party System: 1896 - 1932
Republican Party dominates, both parties continue
Democratic Party: "wet", anti-Prohibition
Republican Party: "dry", pro-Prohibition
Fifth Party System: 1932 -
The New Deal Coalition.
Both parties continue.
However, historians of US political history argue about whether it still continues, or whether it has ended and a Sixth Party System has emerged. Part of the problem is that the transition has been very gradual, and not as fast as the previous transitions have been, with the previously-dominant party losing big in the House twice in a row.
There has been a major realignment over the last half century. Southern Democrats have moved to the Republican Party, while Northern states have become more and more Democratic. This realignment started back when the Democratic Party started to support the black civil-rights movement, and it has continued ever since, with such events as the recent resignation of Maine Republican Senator Olympia Snowe.
As the Republican Party goes farther in changing from the party of Abraham Lincoln to the party of Jefferson Davis, it misses an opportunity to get additional voters: Hispanics. The Republicans could appeal to them with social conservativism and anti-welfarism, but instead it prefers to associate itself with those who suspect Hispanics of mostly being illegal immigrants if not common criminals. This increases the risk that the Republicans could go the way of the Federalists or the Whigs: gradually dwindling into irrelevance.
It's interesting to try to fit the party systems into the Schlesingers' history cycles. A new party system starts at the start of each of their liberal periods or shortly before, and continues for one of their liberal-conservative cycles. However, the fifth one has continued into a second liberal-conservative cycle, gradually turning into a possible sixth one.
So I think that the United States is due for another political upheaval.