OOC: The "40-years War" could have been the name for a long term proxy conflict ala the Cold War, with outside powers fostering unrest and conflict in a divided Germany. That even fits with the general premise and makes it more similar to the 30 Years War. It doesn't have to be 40 years of all out WWII style Total War, although I imagine it would eventually spiral out of control into a massive Total Global War type thing.
OOC: Well, he ought to change the name of the event, then, I think.
Edit-The problem is, too, is that OTL's Cold War was nowhere near similar to the 30 Years' War, for a variety of reasons(which I try to explain below.)
IC: Yes, but Medieval Modernity's "40 Years War" wasn't like our Cold War in the least. In fact, Have you read the book? The beginning of the story didn't even involve nukes but a single mysterious magnetic event which destroyed all of the world's connected electronics at 7:53 pm GMT, September 15, 2021.
The book largely took place in the 24th Century in a post-apocalyptic Europe, in which a Cold War scenario would not even be possible, at least not at the time in which the novels took place.
OOC: (Okay, I'll admit it, I largely ripped off the opening from the fictional novel from the real well-known Steve Stirling series, "Island in a Sea of Time", and it's twin, "Dies the Fire".)
@Helios: The problem is, as noted above, you simply cannot plausibly have a 30 Years War equivalent in the modern age; there are things like chemical weapons and such that were not even conceived of in the Renaissance age. In fact, OTL's WWI lasted for only four years(and wasn't quite as intense as WWII) and look how badly it affected much of Europe, particularly where the worst fighting was.
A proxy conflict lasting 40 years, like a worse & nastier version of OTL's Cold War shenanigans, would certainly be doable, but it wouldn't be anywhere near similar to the 30 Years' War; OTL's Cold War did not involve any actual conflict between the USSR and U.S.; The 30 Years War, did indeed see direct conflict at times.(any actual sustained conflict lasting that long, even if far lower in intensity than OTL's WWII, would badly wreck much of Europe, even in half the time. And that's without nukes.) and thus this is why I suggested a name change of said event if that's what the OP really intended.
Sorry if I can't explain this any better, btw. If anyone would like to try to come up with a better explanation, they are more than welcome.
