Under Article III of the Constitution, citizens could sue states in federal court. The Eleventh Amendment made it so that states could only be sued in state courts. The Eleventh Amendment protected state sovereignty and provided for what is known as the doctrine of sovereign immunity.
The 11th Amendment gave more power to the states. http://www.csc.noaa.gov/ptd/module08/lesson01/0801.htm
This video talks about the sometimes tragic downfalls of sovereign immunity. This video tells the story of Haseeb, a resident of one of the nation's institutions for the mentally disabled. Haseeb was heavily assaulted by a caretaker. Haseeb's family has not been able to seek justice for Haseeb because of their inability to sue due to state sovereign immunity. Many time citizens suffer at the expense of state sovereign immunity, which is protected by the 11th Amendment. This needs to be reexamined.