Start your game as normal, with approximately 3 houses, 2 farms, 2 wells, a water purifier if possible, an ancillary a lumber shack and a mining facility. You will want to build up as much wood and stone as you can before your world becomes corrupted. You are going to have to be building a lot of fire pits and walls later, so if you can manage to get rock and wood storages going, do that.

When the corruption appears on your map, you will want to use those stored resources and whatever your god-hand can grab, to build fire pits to push your buildable area toward the corrupted land.

When you have gotten to within about (1/3 of the map diameter) away from the origin point of the corruption, you will need to start building straight toward the edges of the map. Your goal here, is to create an influence wall so that the corruption cannot spread past the point where your fires contact the edge of the map. This will also mean that you will have at least one fire pit on the outer most edge of the map, to ensure proper containment.

*The reason you need to stop a certain distance away from the corrupted land is because, if you do not, it will likely grow faster than you can contain it. Also because the monsters will not attack fire pits although corrupted Buildings/towers will.

At this point, you can slow down a little bit and focus on your other economy buildings. I recommend building wood,stone, and crystal golem combobulators. this will help in your next section.

Now that you have successfully contained the corruption, you will need to start pushing it back. this will be done by building fire pits on the leading edge of your buildable area on the corrupted side and having them push back the corrupted influence.

When you have pushed the corrupted land back far enough that it starts to get angry and raise the threat level (red bar at the top of the screen), you will want to wall it in and funnel the monsters into a kill-zone for whatever selection of defenses that you feel appropriate. While you are building your walls, you will want to put fire pits IN them so that your influence does not get blocked off.

I personally recommend a mix of towers and golems, in order to save your population from having to fight.

For a quick reference, if you divide the region into a 3x3 grid, the corrupted land should get "angry" when it has been pushed to about 1 grid square of the map.

Now that you have contained and suppressed the corruption and monsters, you can now move into the final stage, Exterminating them.

While continuing to apply pressure in the form of combat golems and human hunters, you will need to build more fire pits, encroaching on the corruption as it is pushed back by the influence generated. This will cause monsters to spawn with increasing frequency, so you will need a good defensive set up.

*Fire elementals can be dropped directly into water and it will slowly kill them. Specters can be dropped into a cullis gate and used to fuel your abilities.

If there are mountains in the way, you will likely have to carve through them "by hand" with your own god-powers. If you do not, you will likely not be able to get to all of the corrupted land.

Continue pushing back against the corruption until it has been completely pushed off of the map and monsters no longer spawn.

Now that you have achieved complete domination of the map, you will want to deconstruct SOME of the fire pits that you used, in order to regain those building slots. It is important to ONLY deconstruct those that are OUTSIDE of your walled-in section, as it may be possible for the corrupted land to take hold again, and by this point, if there is even a single square of it, it will likely spawn a neverending stream of highly powered monsters.

Since there are no more monsters spawning (except for the occasional trashy slime or ghouls from a failed resurrection), you are free to build your population and city size as large as it can go. This will be useful in securing other regions, because you will be able to send 50-60 settlers to start each new region with a tremendous amount of supplies, assuming you have built the migration way station and courier station (I recommend 2 of each).

Using this technique, it should be possible to completely dominate the map no matter if you are starting with a completely new world, or you have lost every region but ONE. You just have to secure one region, and you will have the capacity to take or retake the rest.

Enjoy your inevitable victory!