Parliamentary systems of other countries usually have the advantages of lessons learned since the American revolution. The necessary feature of the American system is countervailing powers, but as a uniparty for corporations or one weakened, it ceases to function and cannot be easily reformed or competed against with a new party. These are flaws addressed to some degree by parliamentary systems where new party(ies) can challenge incumbents more easily.

There are plenty of examples of democracies which began after the American Revolution, and subsequently devolved to single-party states.