Yokkaichi, located on Honshu Island in Japan midway between Tokyo and Kyoto, became an early center of industrial development due to its favorable port conditions. After World War II, Japanese policymakers deemed the war-devastated city well-suited for the petrochemical industry and began developing industrial complexes. Starting with an oil refinery in 1956, various petrochemical plants were built, and the complex began full operations in 1959. As production ramped up, local children became more susceptible to colds and had difficulty recovering. Residents gradually began coughing, and some even experienced severe breathing problems.