One of the most infamous legal challenges to sampled music was MARRS "Pump Up the Volume" in the 1980s, and that was preceded by other famous cases. Not sure why you think that started in the 1990s.

This is nitpicky. The MARRS case was 1987, and Biz Markie and Vanilla Ice are way higher on the list in terms of actually getting attention on the issue and influencing culture.