What does this quote mean?
Seems pretty much self explanatory. There is a high tension among the populace, and some stimulus will set them off into some sort of fighting/battle.
It seems pretty clear. It helps to know that Passy lived from 1822- 1912 (easily googlable). That was right before WWI, which was in fact, a flash that blew Europe sky high. He was saying that there was a lot of tensions among the countries in Europe- each was angry at the other. The "unpreventable" spark was the killing of Archduke Ferdinand. Vengeance for that act started a war that engulfed most of Europe.
The bible teaches us that the governments of the world. will turn on religion. So it will be religion that will be turned on .