Discussion (29 points, 6 days ago, 21 comments) https://news.ycombinator.com/item?id=43722816

"They're having a major drought. Hey, here's an idea: Let's go invade them, when there's no food for us to take!"

But if you mean it as a conquest instead of a resource raid, then maybe it makes sense, because you don't expect the drought will last forever. So invade while they're weak and disorganized, and then try to hold it after the rain comes back.