There are, moreover, two considerations particularly applicable to the federal system of America, which place that system in a very interesting point of view. First, in a single republic, all the power surrendered by the people is submitted to the administration of a single government; and the usurpations are guarded against by a division of the government into distinct and separate departments.
In the compound republic of America, the power surrendered by the people is first divided between two distinct governments, and then the portion allotted to each subdivided among distinct and separate departments. Hence a double security arises to the rights of the people. The different governments will control each other, at the same time that each will be controlled by itself.
Second, it is of great importance in a republic not only to guard the society against the oppression of its rulers, but to guard one part of the society against the injustice of the other part. Different interests necessarily exist in different classes of citizens. If a majority be united by a common interest, the rights of the minority will be insecure.
The Constitution of the United States divides the federal government into three branches to ensure a central government in which no individual or group gains too much control:
Legislative – Makes laws (Congress)
Executive – Carries out laws (President, Vice President, Cabinet)
Judicial – Evaluates laws (Supreme Court and Other Courts)
Each branch of government can change acts of the other branches as follows:
The president can veto laws passed by Congress.
Congress confirms or rejects the president's appointments and can remove the president from office in exceptional circumstances.
The justices of the Supreme Court, who can overturn unconstitutional laws, are appointed by the president and confirmed by the Senate.
Learn more about the Branches of Government at USA.gov.