Indeed. Part of how they have done this is by taking over the state legislatures (both parties), and passing laws and regulations at the Secretary of State level that make it extremely difficult for third-parties and independents to run for federal office. For example, in Texas, a person wanting to run as an independent candidate for president needs to get 80k signatures on a petition by people who voted in neither party primary. Except they will dispute as many signatures as possible, so it's more like 120k needed. Also, you have 69 days to do it!

Both parties are corporations and are part of the problem. They circled the wagons when Ross Perot scared the shit out of them in 92, and the League of Women Voters withdrew from doing the debates because of how unfair they were becoming.