Gary, more affectionately known as Stephane, hated stepping on snails. But that's not important. In fact, Gary, and his curious nickname, have absolutely no importance in this story from this paragraph on, whatsoever. What's important is that snails don't like Gary, or Stephane, or anyone else, for that matter, stepping on them.
For as long as the oldest living snail could remember, the snails had been stepped on by humans. "As long as the oldest living snail could remember" wasn't actually all that long, but they knew that this had been going on since before the oldest snail came around, too, so they pretty much guessed that it had been going on for a good amount of time.
Temporal issues and speech-impossibilites aside, the snails had been talking about doing something about it for almost an equal amount of time. The thing was, the more radical thinkers, who just wanted to get out there and do something about it, were generally the ones that got stepped on in the first place. They quickly learned that the humans had no qualms with squishing snail protestors. It was a heinous crime, and one that could not go unpunished.
Sometime after this initial decision, it was discovered that snail weaponry had no effect on humans. Or anyone, for that matter; not even snails. This led to an internal investigation in the weapons industry, and eventually to an official name change; calling it weaponry was deemed misleading, so they named them 'funsticks' instead and now frequently use them in children's games.
Anyway, after the usual methods of conflict resolution, i.e. peace and violence, were proven to be extremely useless, they began to devise different methods of exacting their revenge. When exactly it became a quest for revenge and not simply safety is unclear, but some think it came along when a snail was stepped on. The others maintain that these 'some' are pretty dense and give snails in general a bad name.
The snail government (which was never the same for long due to countless assassinations by humans whilst travelling) met one fateful day to decide once and for all what they would do to resolve this issue. Many ideas were thrown around, but eventually they narrowed it down to three.