That means the powers aren't balanced enough. In USA I have the impression way too much power lies with 1 person from 1 party. In a democracy, absolute majorities should always be avoided in the most powerful places and policy should always remain the outcome (compromise) of talks between many different parties. The elections serve to point out how strongly represented every faction is, but no 1 faction should ever get near the amount of absolute control it has in the USA. Fact a 3rd party can't arise means the democracy is functionally paralysed, not functioning in democratic way.