Wow, sounds like a Khmer invasion might actually be pretty popular.
It probably wouldn't be terribly hard to mod in either, if someone wants to show Paradox how to properly make invader game options. Here's an example where Khmer can either show up and invade India first, or attempt to take over China and then follow up with India.
Khmer India Invasion
- Off (Khmer never invades India, but their flavor events and potential China invasion are active)
- Always (Khmer will always invade India)
- Low chance (Khmer invasion only has a chance of triggering each game independent of China)
- High chance (Khmer invasion has a small chance of not triggering each game independent of China)
- Follow up (Khmer's invasion will occur as a followup to successfully invading China)
Invasion time:
- ~12-13 century
- 200 years after game starts
- 300 years after game starts
- Semi-random, bell-curved around 1300
- Random
Khmer religion
- Hindu
- Trade influences (Randomly chooses the religion of one of the religions on trade posts bordering the Indian ocean other than Jain)
- Randomized (Most likely Hindu, but could be Buddhist, Toaist, Nestorian, Miaphysite, Sunni, or Shia)