The Civil Rights Act banning discrimination because of a person's color, race, national origin, religion or sex was passed in 1964, and this was a landmark piece of legislation that many argued took far too long to pass.
In the late 1800s, workers organized unions to solve their problems. Their problems were low wages and unsafe working conditions. First, workers formed local unions in single factories. These unions used strikes to try to force employers to increase wages or make working conditions safer.
Answer:
John Locke's support for the principle of popular sovereignty.
The clause is really a state's rights clause. A state may not pass a law that makes something illegal that was legal before the law was passed. In other words if a state suddenly passed a law that said it is no longer legal to park your car in front of any government building, but it was legal to do so yesterday, the police cannot come to your door and issue a ticket for parking in front of a government building because you did it yesterday.
The constitution actually uses the phrase ex post facto law in Article 1 Section 10 Clause 1.