Just because Israel's fearless leader Joshua is dead doesn't mean they're gonna let those Canaanites off the hook. Those guys have got to go. Otherwise Israel might be tempted by their sparkly idol gods.
God tells the tribe of Judah to lead the attack on the Canaanites. The tribe of Simeon comes along, too.
They go totally berserk in Bezek and kill 10,000 men.
They also capture the king of Bezek. And cut off his thumbs and big toes (ouch).
He'd done the same thing to 70 other kings so, y'know, karma.