Agile is a refinement of Waterfall. I think of it as the white water rafting SDLC of waterfall.
The minute sticky notes in swim lanes and informal diagramming were replced by heavyweight, middle-managers (-cough- "agile coach") - waterfall is back.
Rational is one factor of many that brought IBM to its knees -(WARP-OS2) being a contemporary.
It was Rational software pushing their process and CASE tools.
It was an awful, inefficient and bureaucratic process that made it easy to write contracts about deliverables while delivering mostly no actual value to the customers.