Obviously, despite what they'd like you to think, they didn't just save up their meager saccharine royalties until they owned most of the planet. During the 20th century, Monsanto was a herbicide manufacturer, and their most successful product is known to this day only by its code name, Agent Orange. Yes, that Agent Orange (not the one from Reservoir Dogs). During the Vietnam War, the U.S. government decided that the best way to drive Viet Cong militants out of their forest hiding spots was to kill all of the forests in Vietnam. To find out how, they asked Monsanto, who simply tented their fingers and hissed "leave it to us."
"We do not tolerate failure."
To call Agent Orange a herbicide is of course to give it too little credit, as Monsanto achieved their goal of "killing all the plants" by inventing a chemical that would kill every life form that touched it or saw it or thought about it too hard.
Since then, Monsanto has been the target of endless lawsuits from families of the million-odd people who were killed or deformed by Agent Orange, but Monsanto's stock response has always been "We were forced to do it. Also, Agent Orange is harmless." Lately, this has been followed by "Buy our corn."