How Many Kings Did the Israelites Kill in Their Conquest of the Promised Land?

A very important question and the answer can be found in 
the book of Joshua.  First off, the Hebrews, being led by 
the LORD God with Joshua as their commander 
conquered seven peoples who were living in Canaan.  
These included the Canaanites, Hittites, Hivites, Perizzites,
 Girgashites, Amorites, and the Jebusites (Joshua 3).  
Whats more, these races were some truly powerful peoples 
in the ancient world during this time (1400 BC) and had large prosperous cities.  
As for the total amount of kings slain during this blitzkrieg of an invasion, 31 total were killed (Joshua 12) during the Hebrew onslaught. A quite significant number.