If you look at the political systems of other countries, you'll find some countries with more political parties than the US, and others with less, ie, dictatorships.
Generally there seems to be about 6 mainstream viewpoints.
Traditional left. This would be the Labour Party in the UK, the SPD in Germany, the PSOE in Spain and this party would be one of the two main parties.
Traditional right. This would be the Tories int he UK, the CDU/CSU in the Germany and the PP in Spain and also one of the two main parties.
We could see that these two sorts of parties are akin to the Republicans and Democrats.
Then you have center left or center right parties. In the UK this might be the Liberal Democrats on the left side of the FDP which is center right in Germany.
Then you have environmental left. Usually called the Green Party.
Then maybe you have socialist parties. In the UK this is a subsection of the Labour Party, Corbyn being one, in Germany they have a separate party.
Also you can have further right parties. Sometimes these are special interest, like UKIP in the UK and AfD in Germany.
Beyond this, less mainstream would be Communist and Fascist parties.
Potentially you have religious parties where the mainstream parties aren't religious enough.
Also you can have special interest parties. Like farmer parties.
If you have Proportional Representation sometimes different interest groups will join together.
The problem in the US is there are only two lots of representation. You either get Republican or Democrat.
If you could have more choice, what sort of party would you vote for in an election?
More moderate. But my big question here is, in some countries those parties, when elected, form "coalitions" in order to lead. I don't think it's optional--they seem to need to in order to get things done. How does that work? It would certainly be a more cooperative form of government than what we have right now.
That would be great. It would isolate the extremist wings, since no one would want to work and play with them. Or at least one would hope not.
So, in Germany for example, it used to be the liberal SPD and the Greens who got together. They'd have to form a deal, so the Greens would get some things they wanted, in exchange for supporting the SPD's stuff.
The CDU/CSU would form with the FDP.
It's changed, it's been SPD and CDU/CSU together in a grand coalition. Essentially they hammer out a deal of how to work together, and it works.
Politicians can't go far out wacko, because it just doesn't get them far, though that option is still available for those who want to vote it.