Let's talk about why the United States has a 2-party system. If you're American and paid attention in Government class you probably have some idea. There are two big reasons for this. One is the cause and the other emerges from that fact.
The nature of elections in the U.S. is whoever gets the most votes wins everything. 50% plus one is basically the same as winning 100% of the votes. This creates an environment where factions who share some similar ideology join together and form political parties. Since the goal is to get to 50% plus one, you arrive at having two major political parties at any given time.
If one were to take apart the modern Democratic party, there would probably be quite a few individual factions. Everything from Socialists to socially conservative Democrats exist within the party. They form an alliance because each faction individually would have no chance at governing in our system.
Because two parties become powerful they make the laws to aid those parties staying in power. It is easy for a Republican or Democrat to get on the ballot, but it is very challenging for a third party candidate. The two parties also become fundraising and logistical juggernauts, because they hold the power and are sure victors in elections. This makes serious competition from a third party nearly impossible
The U.S. and big and diverse place, so the lack of regional parties is surprising to some. As the nation grew the two main parties grew with it. A big part of that is the power the parties already held at a Federal level (and their role in creating that expansion.) However, I think the main reason is the Presidency.
In the U.S. we elect our head of state in its own elections. Unlike in parliamentary systems where a Prime Minister only has to win his seat*, the American President has to win a National victory. And while it is easy to dismiss the executive power of the Presidency, it is still an incredibly powerful position to hold. The President is a big deal constitutionally, but more importantly there is no position so significant culturally on the earth
A party with no chance of holding the presidency quickly loses relevance nationally. That inevitably leads to that party have no relevance locally, because of Federalism. The Federal Democrats will give scraps to the state Democrats who will give scraps to the local Democrats.
I don't believe there will ever be a time where a third party can hold prominence in the U.S. One of the two main parties today could die and be replaced, but the system will not support a third party for very long.
Thanks for reading
*It is more complicated than that, but I wanna keep it simple, because that has little to do with the point.