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This post is in response to the question "Throughout the United States history, why does Federalism work or not work based on your opinion?" posed by 
Federalism has served many critical purposes since its inception. In the federalist papers, I believe it was Madison that wrote about a very specific purpose of state sovereignty—a check on federal government power. While we do have checks and balances in place on a federal and state level through the different branches of government (executive, legislative, and judicial), federalism allows for states to have control over their own population for the most part. Article 8 of the constitution lays out the specific functions of the federal government and all practices outside of those functions are reserved rights of the states. This means that anything outside of the listed rights of the federal government are reserved or implied rights that the states hold sovereignty over. This has shifted since the conception of the constitution since the Supreme Court makes decisions that then serve as precedent for future decisions and the President of the United States has the power of executive decisions. Federalism allows for states to govern their citizenry in ways that are regionally different than the federal government does. By allowing states to have sovereignty, we gain the ability for more U.S. citizens to be accurately represented. Federal governments that govern a large population and a large surface area of land can often make sweeping universal laws that do not account for regional differences. The needs of urban New York are different than rural Oklahoma. Even things as simple as regional topography can affect the implementation and cost of federal laws, so state freedom to control certain things accounts for these differences across the U.S. that may not have been considered by politicians in the National government. There are some drawbacks to state sovereignty however as without intervention, minority populations within states may be further marginalized and lose access to certain rights.