There probably lots of way to look at it.
The Zho are astrologicaly locked in, and cant expand anymore spingward. They're idealogically opposed to the Imperium. The Imperium is an aggressive expansionist power.
So there never been a peace, just an armistice. Even though the gaps between the ffw are longer, i suspect it just takes longer to rebuild numbers and go again.
In not happy with the run around when I’m asking a simple question about a in game even. I’m sure the imperium considered the day the first Zhodani warship crosses the boarder as the start of the war.
OTU wants ambiguity similar to real life.
Not having an exact date or reason why is a reflection to that.
Like for OTU we have the concept 5 major races. Which escapes me. Valani, Solomani, Zhodani, Aslan and Vargr are the races noted in charterd space to have invented Jump independently.
This is a politcol list. Being on that list is a matter of prestiege and politcal and military power.
So while Vargr, And Solo, Zho and Valani manage to invent the jumpdrive.
The Aslan did not. They were introduce the technology (by whom I forget), and manage to extraplate it from there. Which means they shouldnt be counted. However Aslan as a politcal body promotes and protects bbeing consider as such.
And we know its not a list based on demonstrable history.
The K'kree or Hiver arent on there, the same with Droyne, who've had it the longest at several hundred thousand years. Droyne no longer want to be a major politcal power. So they arent counted.
Going back to WW2. I personally argue that WW2 started when Imperial Japan invaded Mainland China in 1931. There were several involved nations. The splinter nations of China, Japan, Russia, Germany and the US. And there was minor involved with various other South Pacific countries. I feel that stating that WW2 started with Archduke is too eurocentrinic.
When FFW5 start? Probably a couple years after FFW4, with continued social, economic manlipulations, corporate and state esponiages and paying vargr pirates to be annoying. The actual declartion of war, is just a nice thing to do, but doesnt actually mean when the war started.
Like the Zho timed the delivery of the war declaration to coincide with their jump fleet openly attacking Imperial ships and planets.
Even if we want to take a very narrow view, then we cant actually take that date.
The Zho moving their assests to invade the 3I is when it really started and that was at least 7 days before the Ships jumped in. And probably a year before that to get all the assests into place.