Complex sentence: However, starting in 1941, a series of laws prohibited certain discriminatory firings-that is, in almost all US states, and employer can fire an employee for any reason, as long as it isn't an illegal reason.
Split into simpler sentences: However, starting in 1941, a series of laws prohibited certain discriminatory firings. That is, in almost all US states, an employer can still fire an employee for no or any reason, as long as it isn't an illegal reason.