they even call it "a two-party system"
Not part of the constitution, and theoretically a third party could gain enough support to receive the same automatic ballot space that the two parties have....
But, despite your deranged thinking the two party system is not a big conspiracy... there are issues where both parties agree with each other and not a majority of citizens and that's always a problem (except in russia where you do what the government tells you and don't even think about having your own opinion about it).
In general each party is more like a big coalition of minor parties and sometimes a chunk of one flakes off and joins the other (the classic example being southern conservatives abandoning the democratic party for the republicans in the 1970s).
A big problem with the American system is that it runs on donations and rich donors with an agenda can disrupt things. Soros funded prosecutors are a real thing and they cause a lot of damage (the agenda is to lower property values so that financial interests can buy them).