The Slag Plains are a region of North America after the Great Nuclear War. It extends from Hamilton, ON, to Oshawa, ON.
Pre-War, the Slag Plains were one continuous metro, one of the densest population centers in Canada. The area was near-completely leveled by nuclear weapons, the ground blackened. The rubble became rolling hills, channels of rivers, and swampy heaths. But the plethora of metals used to build the old world remained in the ground, and this region is a rich source of steel, copper, and other metals.
As such, this land was colonized by intrepid individuals who pulled this metal from the earth and sold it at steep prices. These individuals lived in small ramshackle communities called Steel Boomtowns. New trails came into use, and metal flowed from this region to Owen, Niagara, and hence to the rest of the Great Lakes.
Niagara attempted to colonize the Slag Plains in 1978, which prompted Owen to send one of his prime lieutenants to build a forward base in order to secure the territory. This forward base is called Ronto, and it's construction took less than a year. Through the use of provocation, Owen was able to coax Niagara into a war, which ended in victory for the Owenites. Since then, Owen has had control of the majority of the plains.
Mining operations have not ceased, but almost no Niagarans are allowed into the territory, which has severely stunted Niagara's slag trade.