Wow Isengard got captured in 8 turns...

[Gigan]

I decided to play without garrison script and Rohan captures Isengard in 8 turns Enabling the garrison script makes the game a slow grind yet disabling it means the balance is ed up

[k/t]

Change the script so it fires only when an AI faction besieges another AI faction.

[Aragon150]

make the ai less aggressive at first or disable stack spam 2

[BigHairyMelon]

I'm also playing without the garrison script and the same happened for me. Rohan took it, however Isengard soon took it back once Mordor started beating on Rohan. Give it time, when Mordor gets involved Rohan will most likely crumble without aid.