After which significant event were many chemical insecticides developed?

The development of many chemical insecticides can be traced back to significant advancements that occurred during and after World War II. The war spurred innovative research and allowed for the production of synthetic compounds that could effectively target pests. This period saw the introduction of DDT and other pesticides, which were initially used for military purposes but later adapted for agricultural use to protect crops from various pests.

Although World War I and other historical events led to some developments in chemicals and technology, it was primarily the needs arising from World War II that catalyzed the widespread research and production of chemical insecticides on a large scale. Thus, the correct context places the developments post-World War II as foundational in the rise of modern chemical insecticides.