The members of the Constitutional Convention signed the United States Constitution on September 17, 1787 in Philadelphia, Pennsylvania. The Constitutional Convention convened in response to dissatisfaction with the Articles of Confederation and the need for a strong centralized government. After four months of secret debate and many compromises, the proposed Constitution was submitted to the states for approval. Although the vote was close in some states, the Constitution was eventually ratified and the new Federal government came into existence in 1789. The Constitution established the U.S. government as it exists today.
In order to ensure popular sovereignty and to prevent a tyrannical form of government, the U.S. Constitution creates two different kinds of separation of powers, intended to serve as a check on the power of the national government and the states. The first and best-known of the separation of powers is the series of checks and balances established between the three branches of government: Executive, Legislative and the Judiciary.
The second type of separation of powers–federalism–is equally important in the nation's attempt “to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity". Federalism grants separate powers to the federal and state governments. While the Constitution assigns specific powers to Congress, the states retain much of their sovereignty to pass laws as they see fit.
Beyond establishing a representative form of government at the national level (with the House of Representatives being directly elected by the people), the Constitution also mandates that the federal government guarantee that all states have a “republican form of government." Although the Constitution does not specifically define this term, it is generally understood to require states to rely on a representative form of government at the state level.
In 1964, the U.S. Supreme Court ruled that the Constitution's Fourteenth Amendment requires states to establish state legislative electoral districts roughly equal in population based on the principle of “one person, one vote" (Reynolds v. Sims). The decision had a major impact on representation in state legislatures, as prior to the case, numerous state legislative chambers had districts containing unequal populations.
The Constitution of the United States does not directly mention local governments. Instead, under the Tenth Amendment, the power to establish local governments and manage state-local relations within each state is reserved to the States.