Until Einstein, no one could understand why the speed of light was always the same regardless of the speed of the observer. The concept of space-time had already been around. The speed of light had already been determined. What Einstein did was introduce that space and time are relative to the speed of light. Time could slow down, space could contract, from an observer’s point of reference. Only the speed of light (through a vacuum) was absolute, which made everyone think “Oh yeah. I never thought of that. He’s right, by George”. So Einstein took a mystery and solved it. Put the puzzle pieces together, as it were.
“Until Einstein, no one could understand why the speed of light was always the same regardless of the speed of the observer. “
They didn’t have the tools to think that.
“The concept of space-time had already been around. The speed of light had already been determined.”
Space-time was developed based on Special Relativity postulates.