I was able to complete this achievement using the very first level in the Empire Campaign. You start with a cannon on the high ground within firing range of every CPU player.
The CPU AI will usually place harvesters such that you soon end up on islands with nothing but the cannons you started with. You too should place the harvesters in your territory to do the same.
Of note, you are allowed to build a carrier, or win one from an enemy, so long as you do NOT use it. I find it helpful to build a carrier as it changes the AI strategy to be a little more defensive - they won't leave their islands undefended if they believe you are going to fly over.