Without Einstein's equation research the splitting of the atomic nucleus could not have evolved the way it did. Although there was a notion that mass contained an inherent energy the exact relationship between the two was not clear.
In 1905 Einstein proved that energy and matter are linked
in the most famous relationship in physics:
This equation predicted an evolution of energy roughly a million times more
efficient than that obtained by ordinary physiochemical means.
Furthermore, the mystery of why a star, or the sun, could burn brightly for billions of years could be explained by estimating the mass of the sun and then calculating the potential energy that could be released, namely the mass of the sun (or more precisely certain elements of the sun) multiplied by the square of the speed of light.