"The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people." - The U.S. Constitution
The amendment says that the Federal Government only has powers granted to them specifically granted by the Constitution. Powers that include, the power to declare war, to regulate interstate business activities, and others.
The 10th amendment says that any power not listed in the Constitution, is reserved to the states or the people.
The tenth amendment was added to the Constitution to limit the Federal Governnments power, because they did not want the type of government that the British had exercised over them.
Adoption of the Constitution of 1787 was opposed by a number of well-known patriots including Patrick Henry, Samuel Adams, Thomas Jefferson, and others . They passionately argued that the Constitution would eventually lead to a strong, centralized state power which would destroy the individual liberty of the People. Many in this movement were given the poorly-named tag “Anti-Federalists.” So they added the tenth amendment.
The tenth amendment was ratified December 15, 1791. Along with the Bill of Rights.
After the Civil War, the tenth Amendment was virtualy suspended, but in 1883, it regained its power, other than that, no changes were made.