The typical phrase is “infantry wins battles, logistics wins wars.” It gets at the same idea as you.

https://www.czdefence.com/article/infantry-wins-battles-logi....

That's the phrase I had in mind when I wrote it. I decided to extend it based on the experience of Pyrrhus :)

It was religion that stopped the Mongols. One of their leaders converted to Islam and broke up their empire.

Completely incorrect. The Mongol social structure did that without religion. Like most nomadic peoples, inheritance rules split the ownership amongst a leader’s sons, fairly equally. This is because they had people and herds, not land (hence, nomads), so it was the most sensible way of doing it.

This, mixed with the fact that Russia and the Middle East are thousands of miles away from the Mongolian and Chinese capitals made it inevitable that a leader on one side of the empire would ignore their overlord on the other side. Thus, the empire would fracture quickly (and pretty much did as soon as the family ties to Genghis Khan were loose enough).

Being good at religion allows you to be happy for an eternity.

Being good at religion allows you to start war after war

Neither statement is true. You can’t fanatic your way out of a weak economic base for long and plenty of non-religious people live happy fulfilling lives.