Middle-earth: Shadow of War

I found a guide on Eurogamer.com that helps a lot.

www.eurogamer.net/articles/2017-10-13-shadow-of-war-the-shadow-wars-explained-how-to-get-true-ending-complete-endgame-4823

The Shadow Wars take place after the ending of the game and the Capture of Minas Morgul. It's the set of quests that hide "the true ending" cutscene.

There are ten rounds to the series of attacks on your strongholds. It'a basically defending them until all eight of the Nazgul warchiefs are dead.
Best thing to do in each city is to make a combo of effects, what I found works for me is different to what other guides online, so you may have to experimene a bit.
Metal Walls, Cursed seige equipment, Fire mines, poison spouts and Drake traps are what I used to best effect.

Also, the level of your castle also goes by the level of your Warchiefs and Overlord. You want the highest leveled Orc as your Overlord during the attack. It's wise to assign at least two or three bodyguards to Warcheifs as well. The more damage you can do ti the enemy warchiefs the better.

It's worth noting that you cannot lose any of your Orcs to if you die yourself. They just get ousted from the keep and and you lose control of the citadel. They will die if you repell the attack, however, and in some instances they can even stay dead when you die.
If you loose control of a city (like I did during round three), the game will install an Overlord and six warchiefs. Assign the strongest followers to go to the pitts and set up betrayl missions, just like in the main game. Once recaptured, you've completed the round.
It's a lot easier attacking than defending. But I wouldn't go out your way to kill yourself killed just to do it.

I've also come across that if you don't reach a captain in time before they bleed out, once you loose the keep, they come back for revenge during setting up the attack. I'd advise rebranding them, as they always come back more powerful than when they died. For example, I have an Assassin, Pûg the Poet, he died at level 36 and came back for revenge at level 48, also had an extra Epic trait in his arsenal.

It'a also, worth holding onto your Might metre to ressurect dead captains.

Minas Morgul is the only city that won't come under attack.
There are 10 rounds and 20 defences in total.
Round One: Cirinth Ungol
Round Two: Nurnen
Round Three: Seregost
Round Four: Gorgoroth
Round Five: Cirinth Ungol and Nurnen
Round Six: Seregost and Gorgoroth
Round Seven: Nurnen and Seregost
Round Eight: Nurnen, Cirinth Ungol and Gorgoroth
Round Nine: Cirinth Ungol, Serehost and Gorogoth
Round Ten: All four under attack at once.

Once completed you will see the true ending.

Maybe is it due to a recent update, but my Shadow War Run needed only 3 stages :
- Cirith Ungol
- Nurnen
- Nurnen, Seregost, Gorgoroth

After what, the achievement popped and i was able to see the Cutscene.

All other advice on this topic are of course very useful.

On my side I used a lot the Pit Fight (Champion level) to bring strong captain in the game. I faced them with one of my captain, who has a chance to win. Two possibilities : my captain win, and he grow up very fast, OR he loses, so I dominate the winner to add him to my army. Beware the strong capabilities of the opponent which can be shown with RS before the fight : he must not have "strong will" (i don't know the exact word in english) or you will have to kill or humiliate him.
-> With this technique I was able to quickly get a team of lvl 50+ warlords.

To add on to the above tips....

If you're ever in a situation where you're about to die from a "No Chance" Captain, you can simply hit the Home button on your controller before he kills you and quit out of the game from the Home menu. When you restart, you'll still have your fortress intact. Youll have to do the fortress battle over again, but it sure as hell beats having to infiltrate 6 fucking Warchiefs in order to retake the castle, which can take hours!

*edit*
Due to the changes to microtransactions my solution won't work anymore!
**edit_end*

The guide above is good. There is a loot box trick to get unlimited Loot-Boxes with ingame currency. With these you can get Orcs close to your current level -> No Orc training required.

Here is how:
1. Make sure your latest save is synched to cloud
2. Go to ingame market an buy standard loot boxes with ingame currency (Mirian, spend everything you can)
3. Once purchased, quit to main menu BUT leave the game up and running!!!, go to Dashboard, highlight Shadow of War, press -> Manage game. Choose to delete your save game on console only! Do not delete everywhere!!!!
4. Because you deleted the save, Shadow of War will be closed. Start it.
5. On startup it will sync your cloud save -> You have all your Mirian back and because the loot boxes are saved on WB servers you still have the ones you purchased.
6. Repeat with step 2

THIS DOES NOT WORK WITH PREMIUM CURRENCY!!! as this is stored on WB servers, too!