The Israelites tell God that if he'll be on their side they can take down the king and his army and then "utterly destroy" their attackers. Cheery. So, that's exactly what they do.
Once Bitten, Twice Die
Despite their victory, the people are whining again.
They wonder why God took them away from Egypt (and slavery) just to have them starve to death in this Yahweh-forsaken wasteland.
In other words, there's no food.
This time, God is not so forgiving of their gripes. He sends a whole bunch of poisonous snakes to bite them. Think snakes on a plane are bad? Try snakes on a plain… in the middle of the desert.
The people pretty quickly realize they've been naughty and sinful and ask Moses for help. Moses goes to God, who tells Moses to make a "serpent of bronze" and put it on a pole. If anyone gets bitten by a snake, they can look at the bronze serpent and they won't die. Wait, so there's still snakes all around and they're still biting, but at least no one's gonna die. Gee, thanks, God.
At War With The Amorites
The Israelites keep on travelling through the wilderness (and get some more divine water delivered to them) when finally they come to the place where the Amorites live. Again, Moses asks the king if they can pass through. He gets a big fat, "No!" for his trouble.
But this time, when the Amorites attack, the Israelites get the better of them… and all their lands. Hooray for the spoils of war!
Same thing happens when they run up against the King of Bashan. Israel kills "him, his sons, and all his people, until there was no survivor left." Yikes, guys.