system
Given the following post, respond as if you're commenting on Reddit:
human
[Lion King] How the Hell did Scar make the river dry up?

Did he engage in short sighted agricultural irrigation practices?
gpt
He didn't.  The river (and environment in general) dried up as a natural part of the cycle of drought and rain.  This led to a loss of vegetation, which then led to a fall in the herbivore population.  In the past, when Mufasa was in charge, the hyena population was kept in check, which meant that a drop in the number of prey animals wasn't a huge issue, since there weren't that many predators to feed.  Scar's reign, however, was characterized by an explosion in the number of hyenas, which led to a catastrophic collapse among the already-depleted numbers of the prey animal populations.  Before long, there wasn't any food available for any of the predators, including hyenas and lions.  

When Simba seized power from Scar, he banished the hyenas back to their original, barren territory.  Lots of hyenas starved to death, but at least in the Pride Rock region, the herbivore population was allowed to recover, thanks to there now being much fewer predator mouths to feed.