My go to example for stuff like this is the Labour Party in the UK. For hundreds upon hundreds of years it was a two party country, between the Whigs and the Tories, later the Liberals and Conservatives.

At the turn of the 20th century the working class and trade union movement created their own party, the Labour Party. At the time I’m sure many people said it would be impossible to challenge the existing duopoly, that it was a waste of time to even try, etc etc.

By 1929 they were the largest party in the House of Commons. In 1945 they won the majority. It wasn’t an overnight victory. But a lot of people put in a lot of hard work because they believed a better future was possible and their effort paid off.