The concept of chemical substance as "any material with a definite chemical composition" was introduced in the 18th century, especially by Joseph Proust. However, it was a whole century later when Mass Production allowed use of Chemicals on an industrial scale. Without Chemicals, there would be no artificial fertilizers, no plastics, no advanced drugs or cosmetics... It should be noted though that on the other hand there would be considerably less pollution, and the horrors of chemical warfare cannot be ignored either.