They were first introduced to the US through the British, French, and Spanish colonists. Most of the hogs would be left to run wild and caught when needed. Over the last few hundred years they simply multiplied to such an extent that now they are causing damage to farmland in the billions of dollars annually.
Huh... sounds like the government at work. Different governments, same kind of work. Like the coyote they brought in my area to take care of the rabbit problem, so now we have a coyote problem - or the asian "painted lady" beetles (foreign ladybugs) they brought in to take care of the aphids, but instead they infest my bedroom every winter - or the kudzu, let's not forget the wonderful kudzu vine that was planted everywhere to stop soil erosion, but it didn't stop erosion and it grows inches a day.
Yeah, sounds like the same kind of government at work. Not that I'm anti-government, but they never learn that ole mother nature is just too complex for them to tinker with.