There should be lots of ways the war could be triggered.
The war really could have started in 1905 or so, I think there was some sort of naval crisis off the coast of Morroco, I can't remember the details.
France and Germany were on a collision course. They were going to go for it sooner or later.
England though may not have gotten involved. They were actually not that interested in honoring the alliance with France. They entered the war because of the attrocities committed by the Germans in Belgum. If the Germans had not gone through Belgum, or had not shot civillians, England would have sat it out.
I think the EU2 diplomacy model would handle this ok.
Germany, Italy, Austria in an alliance.
France, Russia, England in an alliance.
England guarantees the independance of Belgum.
Russia guarantees the independence of Serbia.
Random event happens, "Political crisis" Austria gains CB on Serbia.
Austria declares war on Serbia, Russia gains CB on Austria.
Russia declares war on Austria, France honors the alliance and declares war on Austria, England dishonors the alliance. Germany honors the alliance with Russia and declares war on France and Russia. Italy dishonors the alliance.
Germany invades Belgum, England gets CB on German and declares war on Germany.
The only changes you have to make to the EU2 system are these:
**If a country declares war on another country and there is already and alliance at war with that country, the country declaring war automatically joins the alliance.
**If a major nation guarantees the independence of a minor nation, and the minor nation is attacked, then if the guarantor does not declare war on the attacker they take take a massive stability / dissent hit.
The odds of the historical alliances occurring in the game probably won't be that great. At the start of the game, France will be isolated, and England, Germany, Austria, and Russia allied as Napoleon was a recent memory.
Bizmark was able to maintain this for the most part, except the Austrian part, in order to keep France isolated.
France wasn't able to break out of this isolation until Germany let it slip towards the end of the century. If Germany had been able to hold onto the Russian alliance, then France would have gotten squashed in 1914. They almost did it as it was, with the extra troops they would have done it for sure. I think in the game that Germany should have a pretty good chance of holding onto the alliance with Russia. Both countries were still monarchies and the monarchs were related.