Command & Conquer: Red Alert 3

If you finish all the 9 levels of each of the 3 campaigns on normal or hard, you will get this achievement.
Medium is obviously easier than hard, weaker units spawn, the computer is easier to defeat.
The last few levels of every campaign are the hardest.

Some tips:
- It's a lot easier to do this with a friend or just someone else, normally you get a co-commander (computer), having someone else to do this with in co-op helps a lot.
- Learn to know the units and missions, I did this campaign on hard from the beginning, I didn't finish all the missions on first try, after a while you know exactly what to do.
- Use your special abilities, in every campaign you can use special attacks, just fly by or drive by with a unit and use the special abilty on a important building (MCV and vehicle depot first).
- For me, using air units worked the best during the campaign.
(Soviet twinblades, Allies vindicators, Rising Sun Strikers)
They're fast and do massive damage in a short time, but beware of enemy anti air units, they can kill your army in a few seconds.
- Take your time! Even if there is a time limit. Build up defences first (Turrets, anti-air and anti-ground units) and start building up your army till it's big enough to attack.
- You don't have to do the secondary objectives, it's for the other achievement, you can do it on easy as well.


If I'm missing something, just put it in the comments and I will edit the solution.