Argentina used to have a military dictator who held all the power. The country now has a federal form of government. Which aspect of a federal form of government now protects Argentina from the control of a dictator?

It is protected by the fact that it has a system of separation of powers with three branches that control each other and prevent tyrannical behavior from a single branch. They are also separated into local provinces and autonomous regions that are ruled by small scale governments that have some degree of independence and that could easily oppose a new form of tyrannical government.