In short words: Siam did it (well mostly, Mongols did a little too).
In long words: I "did Siam" to them
After many games I developed "multi war - diplomacy over fighting personally strategy".
I often start conflicts with civs not neighbouring with me*, simply to push my neighbours into war through alliance. Main goal is to weaken both neighbour and the next civ. Let's keep strongest civs in balance stretching their forces along many fronts. Their armies are far from my cities fighting each other to death. I do my best to do any fighting only in the end when one side is really weaken. It sometimes mean I have to wait tweny turns to invade my neighbour which was allied with me, because he was goind to lose the war.
*Or maybe more true is to say I declare wars to those who are not able to pay me a lot of money through trade deals. Another factor is enemies' army movement which i constantly track with explorers (and workers before explorers).
This can be interesting and I could describe other examples but let's talk about this China example:
So to start I have to say it didn't go the exactly they way I planned it, but in the end effect was the same (hovewer on much bigger scale as seen on the uploaded map).
First I recognized chinese units moving west to fight some european civ (I don't remember which one, I don't play daily - I started this game in April this year). They were moving mostly through mongol territory due to ROP. Siam got involved in some european conflict as well so they would soon start moving west. I built "human wall" in real life "north-eastern zonal council" of India (simply in east of my mainland territory) starting at the sea, ending in the mountains. This way Siam will start moving units into China to go west through Mongolia as well. And that of course happens (steering enemy movement or mostly blocking it from certain areas is something common in my games).
So after few turns China has it's army in Mongolia and Siam has it's army in China. Great moment to start Siam-China war. I only have to choose who to fight on my own. I go against Siam, because China is paying for my reasources and is more developed civ. I'm little scared Siam will cut off chinese capital**, but what the hell, let's do this! I of course buy China into war and locate my explorers around Siam army to watch what they gonna do.
What doesn't go with the plan is that after I finish my turn, Chinese ship goes into one mine somewhere in Indonesia and now I'm in war against both China and Siam***. And this in fact means it's even better;D Now I go into Alliance againt China with Mognols. So Chinese units start to pillage everything in middle of Mongolia on their way home (which they never gonna reach). Siam however turns back to attack me, but I fight them only few turns and sign peace as soon as I can. But if not Chinese attack I could have been in troubles and forced to fight Siam force on my border. So the whole thing was really risky I must say.
After peace with Siam I just watch Siam fighting China and China fighting Mongolia. Mongols are strongest so they will wipe out chinese units while Siam goes into China terrirtory to pillage roads and raze cities.
There will be short peace period after twenty turns when Siam stops fighting and I finally can go into peace with China (end of alliance with Mongols), but soon after they will attack me once again on the sea, so I will once again send Siam at them. This time for good. Effect is visible on the map. And most of city razing happens already in "full capacity era", so this is why it went empty - all city slots were instantly used somewhere else.
**I often put my defensive units into my allies territory to protect trade route to their capital city, but I had none in China and going there through mountains or with ships was to much setup to wait for this.
***after few turns I reach my record of being at war at the same time with:
- Russia
- Ottomans
- Arabia
- Scandinavia
- Carthage
- China
- Siam
And if remember correctly I was literally fighting only Ottomans on my own then.
So you see Siam-China thing is just a piece of big picture. But I won't write about them all now. I can only say that I managed to push everybody to war so effectively, that world wide tech reaserch simply halted (i don't do my own at all, I only trade and steal).
