Prior to the second world war most homes in America had solid hardwood flooring. Homes were built on raised wooden sub-floors which allowed for solid wood to be installed by nailing the planks into the sub-floor.
When World War II ended in 1945 all the young vets were coming back home. They were getting married and starting families and so the building industry saw a spike in the demand for new homes. New homes needed to be built quickly and inexpensively. So as a result tract housing neighborhoods were developed and concrete slab foundations were developed as a new technology replacing raised wood sub-floors.
This created a problem for the hardwood flooring industry because you could not put solid wood directly on concrete. So the need for new types of flooring grew in demand. More homes were installing linoleum (today known as vinyl) and wall-to-wall carpet.
So the wood flooring industry which lost a tremendous amount of market share basically had to get together and come up with a hardwood floor that could be glued or floated directly on a concrete slab and be resistant to moisture… the Engineered Hardwood Floor was born.