Well technically there are different groups but really in the US there are kind of really only the two.

This is because of how us elections work where splitting tickets to more than 3 people running tends to hurt the most popular side. It's not like parliaments where they build a coalition after people vote.

So if you look at the US senate you have almost all rep or dem and then 1 or 2 independent.

Also looking at voters you do have like the green party but that's not really a thing when talking about presidential or congressional political. Those groups are really just spoiler candidates. You also have independents, not registered for any of them, but that just means they don't get to vote in most primaries, and really then vote Dem or rep.

There has been a move in some areas to move to ranked choice voting. Alaska and Maine have both done this. If this happens nationally it will have a huge boost for those other spoiler parties and likely make a more functional democracy.