What would we see of a devastating interstellar war between alien civilizations within 1000 Ly?
I have two interstellar civilizations, both of which are extremely advanced and within a few thousand light years of earth. They go to war and make some stars explode in the process.
The Combatants
I have in my space setting two civilizations who are extremely, extremely advanced. To get an idea of their capabilities let me list the ones relevant to this discussion. Both sides were capable of causing a star to go super nova, had micro black hole arrays as their "small arm weaponry" and were able to warp from star system to star system by willing it. There is a tech gap between them that is balanced by the less advanced ones, who I will refer to as the Industrials (of whom you can imagine as extremely advanced machines), being much more tenacious than the Archivists. The Archivists, whose design is very serpentine and fuming in blinding energy are ancient beings who really just wanted to collect data on the universe. They predate the empire, but that part of this overbuilt cosmic history isn't important here.
So why are they at war? Here's a bit of context for anyone who needs it.
Context
There is a somewhat complicated history behind why such a cataclysmic war occurred in the first place. Since it's not the meat of my question and really unrefined in terms of completion i'll just say the following long sentence. While humans were figuring out agriculture a powerful, seemingly all encompassing empire spanning the Orion Arm fell apart violently due to a miasma of catastrophes that stem from the Archivists launching a decapitation raid on the empire's oligarchs in response to the empire destroying their observatory world located around a star in the Aquila rift. Said observatory held quite a few Archivists. Given the distance of the named place, you may see why i'm asking this question.
Fast forward a thousand years and the empire is pretty much dead. A procession of events leads the Industrious to have a civilization that is slowly murdered by a cryptic force known as the Celestials who appear on the scene a few centuries after the empire's decapitation. 302
They just start killing anyone who is self-aware and a pain inducing war against a would-be Empire Successor polity called the Eternal Republic which no one but the Celestials won. The Eternal Republic was exterminated, but the Industrious had enough time to go into hiding as the celestials massacred their society as well. Industrious than spent a few millenniums in hiding as the Celestials continued hunting down life that was sensed by them as self-aware, purifying world after world of such life. The Industrious however, rebounded and rebounded hard.
The Industrious deep within the mantle of multiple worlds uninhabitable managed to advance to technological levels that rivaled the Archivists to a degree and begun a uphill crusade against the Celestials, at first being very outnumbered. However the Industrious at this point were militarily far more advanced than the Celestials, meaning they easily fought the Celestials despite being out numbered and rapidly expanded in numbers as they exterminated the Celestials. Once the Celestials were killed off, the Industrious inexplicably turned their weapons and vast military on the Archivists. Thus began the Annihilation.
In the Annihilation (which was a war that only lasted a century), multiple stars were super novae'd. But the Industrious, despite managing to do far more damage to the Archivists than the Empire ever could would lose the war. The Industrious as a species were let off surprisingly easy, being only reduced to a primitive, stone age civilization. The Archivists however, instead of coming to dominate the Orion Arm simply went into further hiding. They still are out there to this day, observing as they always had.
I am aware that by cosmic history has opened way more questions than answers (like about the culture/nature of all these aliens and the way the empire was ran), but I rapidly came to realize a massive, massive trouble with all this star exploding and interstellar massacring:
Wouldn't we have noticed all this?
I ask this since there is no way a war where stars went into supernova in such rapid procession wouldn't be noticed by astronomers and raise tons of questions. The super novae would after all leave behind planetary nebulae in their wake, such as the crab nebula which came from a super nova seen around the world in 1200 AD. The question of super novae also has been bothering me since wouldn't multiple super novas in short procession would cause some very noticeable planetary nebulae complexes? These would be extremely noticeable cosmic features within a thousand light years and their cultural impact may have history altering conditions if I have this in my mind right. 963