<P> Another example of congressional power is its spending power--the ability of Congress to impose taxes and distribute the resulting revenue back to the states (subject to conditions set by Congress). An example of this is the system of federal aid for highways, which include the Interstate Highway System . The system is mandated and largely funded by the federal government, and also serves the interests of the states . By threatening to withhold federal highway funds, Congress has been able to pressure state legislatures to pass a variety of laws . An example is the nationwide legal drinking age of 21, enacted by each state, brought about by the National Minimum Drinking Age Act . Although some objected that this infringes on states' rights, the Supreme Court upheld the practice as a permissible use of the Constitution's Spending Clause in South Dakota v. Dole 483 U.S. 203 (1987). </P> <P> Article V of the Constitution accords states a key role in the process of amending the U.S. Constitution . Amendments may be proposed either by Congress with a two - thirds vote in both the House and the Senate, or by a convention of states called for by two - thirds of the state legislatures . To become part of the Constitution, an amendment must be ratified by either--as determined by Congress--the legislatures of three - quarters of the states or state ratifying conventions in three - quarters of the states . The vote in each state (to either ratify or reject a proposed amendment) carries equal weight, regardless of a state's population or length of time in the Union . </P> <P> Article IV also grants to Congress the authority to admit new states into the Union . Since the establishment of the United States in 1776, the number of states has expanded from the original 13 to 50 . Each new state has been admitted on an equal footing with the existing states . It also forbids the creation of new states from parts of existing states without the consent of both the affected states and Congress . This caveat was designed to give Eastern states that still had Western land claims (including Georgia, North Carolina, and Virginia), to have a veto over whether their western counties could become states, and has served this same function since, whenever a proposal to partition an existing state or states in order that a region within might either join another state or to create a new state has come before Congress . </P> <P> Most of the states admitted to the Union after the original 13 were formed from an organized territory established and governed by Congress in accord with its plenary power under Article IV, Section 3, Clause 2 . The outline for this process was established by the Northwest Ordinance (1787), which predates the ratification of the Constitution . In some cases, an entire territory has become a state; in others some part of a territory has . </P>

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