It was based on Article II of the Articles of confederation,that stated that, " Each state retains its sovereignty, freedom and every Power, Jurisdiction, and right, which is not stated by this confederation expressly delegated to the United States, in congress assembled."
In my own words, the amendment says that if it doesn't say anywhere in the Constitution that the states can't do something, the states have the power to do it.
Bond vs. United States 2011
Carol Anne Bond poisoned, harassed, and threatened her pregnant friend because the father of her baby was her husband. The Supreme Court charged bond with two counts of possessing and using a chemical weapon in violation of a statue and two counts of mail theft. They rejected her arguments because they were violating the tenth amendment. Bond was found guilty and received a 6 year prison sentence.