The World Domination starting level is assigned based on your level. Specifically, your Dominance Rank starts 25 levels below your level. A level 60 player will start with a Dominance Rank of 35. It is unlocked at level 25 with a Dominance Rank of 1.
You unlock new units as you advance in Dominance Rank. These are unlocks, not single units—once you've unlocked a new unit you'll be able to buy it with normal resources. You can use Empire Points to unlock the next rank of unit above what you currently have access to, but you can never unlock more than one level above what you've earned with your Dominance Rank!
Unlocked units can be build in your barracks, shipyard and hangar.
You will automatically be matched up with other players who have a roughly similar Dominance Rank as you, so the fights will offer a challenge. When you defeat an enemy, your Dominance Points will increase. You'll get more points for challenging someone who has a higher Dominance Rank than you, and fewer for picking on someone with a lower Dominance Rank. You can only challenge other players whose rank is up to one rank higher or three ranks lower than you.
Leveling up your World Domination level gives you more points to make your Defense Force stronger.
Your Defense Force is a group of units that your enemies will face when they try to attack you. The total strength of your Defense Force is limited by your Dominance Rank. The higher your Dominance Rank, the higher the total strength your Defense Force is.
The size of the force you can bring to the battle is dependent on your Dominance rank. Your invading force has a maximum strength limit --- the combined total strength of all of your units can't exceed a certain number. This number increases as your Dominance Rank goes up.
The number of Dominance Points you will be awarded per defeated enemy is 100 plus or minus the difference between your Dominance Rank and your opponent's. So if you beat an opponent who is two ranks lower than you, you will be awarded 80 Dominance points. The maximum number of Dominance points you can win is 150 (plus a revenge bonus) and the minimum is 30.
The catch is that when you challenge an enemy, you won't know what his Defense Force is until you have finished deploying your units and press the "Fight" button.
When an enemy challenges your Defense Force and wins, you lose Dominance points. It represents 20-100% of the Dominance points the enemy won. The number of Dominance points you lose is based on the strength of your Defense Force. If you have a strong defense composed of at least 80% of your maximum possible defense strength, you will lose 20% of the Dominance points the enemy won. If you have a weak defense composed of less than 40% of your maximum possible defense force, you will lose 100% of the Dominance points the enemy won. So if the attacker is one rank below you, a win awards the attacker 110 Dominance points. As the losing defender, you will lose 22-110 Dominance points based on the strength of your Defense Force.
You will never lose enough Dominance points to lower your Dominance rank. And once you unlock a unit with Dominance, it is permanently yours even if you fall below what was the initial points required.
When a player challenges you in World Domination and wins, that player gets added to your Rivals List. When that player is your rival, you get 30 extra Dominance points for successfully challenging them in return. Rivals disappear after 24 hours but they can stay for more than a month if the challenger has a higher Dominance Rank.
Your global standing is the percentage of players with more Dominance than you, however this value can be 0% meaning there is less than 1% of players with more WD points.