Millions of workers and youth in the US are fed up with the two parties of the capitalist class: the Republicans and the Democrats. The lack of a mass working-class party leaves voters with little real choice: either vote for one of the ruling class’s parties; cast a protest vote for a tiny third party; or abstain altogether. But why is there no mass workers’ party in the US? Why have past attempts to build one failed? What lessons can we learn from history to change this in the future?