As the Progress Day story clearly showed, Noxus is mapping out Piltover with its eyes set on wanting to conquer it. Good ol'
managed to sniff out one of the mappers but the other is now working for Clan Medarda.
So just like they tried with Ionia, is Piltover next? PS: Will we ever get to see/read stories of the war between Ionia and Noxus?
Piltover Vs Zaun is happening.
I think it will be more a Noxus backed Zuan, not Noxus vs Piltover
[deleted]
No, I think it was mentioned in the lore page that Piltover intentionally refrains from investing in warfare and military grade weaponry. Rather they're purely driven by progress, though they've also demonstrated a callous disregard for the means to achieve those ends, as well as major hubris. But that's a tangent.
However, despite Piltover's goody goody futurology shtick, I honestly believe Zaun is more technologically advanced, and I think it makes more sense that way. Since Zaun has very few ethical boundaries, they can research and manufacture more brutal, efficient technologies that Pilties wouldn't even dream of pursuing. Zaun has also demonstrated a willingness to invest in weaponry, whether it be chemical like Singed, or mechanical like Viktor. Hell, a Zaunite even invented a goddamn time machine.
If Piltover gets invaded by Noxus, I can tell you with absolute certainty that Piltover will lose, and it will not be close. Zaun will definitely play a major role in tipping the scales, though it depends on which side they end up supporting. We might even see a rift in Zaunite allegiances, since they supported Noxus in its invasion against Ionia, but they're also physically and technologically a part of Piltover. We'll find out once they update Zaun lore!
The thing that was interesting to me about Tamara is her complete lack of concern for Zaun. There is no evidence that she had studied the layout of Zaun nearly as heavily as Piltover. Reasoning behind my belief of her disregard is the crap shoot at the beginning of the story. She has no idea what's at the bottom of the shaft and doesn't care much.
This could mean a couple of things.
Given what Caitlyn implies about Noxians we have ample reason to believe that both of these are true.
Whether or not Zaun helps Piltover I doubt that they'll accept one ruler for another. I suspect that a failed Noxian invasion on Piltover will end with more equal footing between Zaun and Piltover, because it's unlikely Piltover could repel a full on attack by Noxus without the support of Zaun.
In honesty in this current world and setting, Noxus hasnt much of a chance to suceed in any conquering as long as Demacia plays as the USA of League and comes to the aid of lower/weaker cities
Demacia + [Insert Ally Here] > Noxus + [Insert Anyone]
Noxus is probably backing elements of possible conflict in Zaun so that either their ally Zaun takes more territory or Piltover wins with considerable damages and Noxus sweeps in and crushes both. Classic Xanatos Gambit tipping the scale so either outcome is victory. Good Job 
Eventually, most likely, yes.
