The Zuma monster grinder did wonders for protecting Terran and Barca. Even if they didn't actively patrol Terran lands, no monster spawn came out of Zuma lands, and any monsters that wandered into there never came back. Realms like Astrum and Niselur didn't have any of that advantage. All those realm-kiling packs we saw the Zuma beating up? Well, everyone else had to deal with them ourselves. I'm not saying that Terran and Barca didn't have to struggle against monsters, but you have to give the Zuma quite a bit of credit for sweeping things clear, even if it was passive.
No, monsters did wander in from Zuma lands. Reduced yes, but we were still fighting them.
Again, the Zuma did not "sweep things clear." They killed many of the monsters that came into their land. They never once to my knowledge moved out and cleared anything beyond their borders.
