How do I set up Invasion Territories?

Make sure on the forge lobby it says the gametype is 'Invasion' or whatever.

Place an item to be the 'base'

Go to object options, shape (may be under Advanced, i can't remember) and set it to the shape of the territory you want. Then set the game tag to INV_obj_1 (iirc)

 

The tag needs to be inv_obj then you set the spawn sequence to two for second tier 3 for third and 1 for first

 

Check out these tutorials, they are very clear and elaborate!
(Make sure to watch all parts on YouTube!)
I hope it will help you setting up Invasion.

Spoiler

Halo Reach Forge: Invasion Tutorial part 1 - YouTube