In the US, we have the most mature democracy on the planet. Thus we have two parties. In the beginning, there were a ton of parties. You needed a score card, and it still didn’t make sense. It was like every candidate was a unique individual, and you had no idea what their history really was.
New-born democracies often start with a dozen parties. In the first few years, these get reduced in half, as the little parties merge with larger parties that share a lot of their positions. These mergers happen for the same reason they happen in business: greater numbers equal more foot soldiers and more power in elections and more money raising, and greater efficiency.
The end of this party consolidation always comes when there are two parties in a democracy (one “party” in non-democracies). And these two parties tussle back and forth, each trying to claim their half, plus a little be more of the center, so they can win.
Inevitably, in this process, a lot of ideas get left out, as the parties seek to position themselves with the greatest chance of winning the coveted center. So people get angry, and in hoping to push their ideas, they try, again and again, to build third parties. These almost never take hold. And even if they do well in one election, their share of the vote has always plummeted in the next election.
The Republicans will not split, because they know this will doom them to irrelevance for the foreseeable future. If Republicans split, the Democrats will be the majority party for as long as the Rs are split. Sure, the more moderate of the R parties will try to become even more moderate, and take over some D territory, but the Ds will still work hard to keep half the population. If the Moderate Rs do cut into D votes, then we’ll see coalition governments, and that would be too weird to predict.
Dems can only dream of an Rep split. That would be such good news for them! But it won’t happen. The Rs will repair their coalition, and maybe grow a little bit more moderate, in order to try to take 51% in the next election.