To take away the ability of the enemy to hide in the jungle terrain, the u. s. used (which we later learned harmed u. s. soldiers who were exposed to it).

Agent Orange

This chemical was used to obscure the jungle and deny the North Vietnamese army the jungle cover that enabled it to attack and maneuver through the terrain of the jungle. It was later discovered that the chemical was not harmless as thought and had a detrimental effect on the U.S soldiers

while it was true that the cotton gin reduced the labor of removing seeds, it did not reduce the need for slaves to grow and pick the cotton.

explanation:

before eli whitney's invention of the cotton gin, picking and cleaning cotton was a slow, labor-intensive job. workers, usually slaves, had to pick the seeds from the cotton fibers by hand. this invention made it possible to grow large amounts of cotton on big farms and make money.