Remnant Anon here, here's a little lore blorp I have for the changelings in my fic.

Pre war: After the defeat of Chrysalis and her hive in their failed invasion of Canterlot, the Changeling hives became more withdrawn and secluded due to fear of Equestrian retaliation and the aftermath of the invasion not only caused Equestria but most of the world to grow more aware of the threat the Changelings prose, within the following decades the Changelings began their industrial revolution developing their own unique technology made out of organic material but even with their unique breakthroughs in science the Hives were still considered technologically and industrially inferior to Equestria and the Zebra empire.

Great War: during the outbreak of the great war the Changeling hives joined the war as an unofficial third party with many of the hives seeing the war to gain power and to crush the battered victor of the war be it Equestria or the Zebra empire these plans however changed dramatically with the creation and distribution of the first megaspells causing the hives to go into overdrive as their plans switched from changeling domination and supremacy to changeling survival and preservation, in preparation of the worst the hives began abducting both Pony and Zebra as nothing more but stockpiling food in preparation of the worst outcome and ordering their infiltrated agents to try and deescalate the war from ending in Balefire Armageddon, but their efforts were for not as the last day came anyway with Hives bunkering down with their communications began quickly breaking down as the Queens gave the last order to their agents who they still had in contact with, survive at any cost and make it back to the hive at any cost.

Post war: Following the Last day the Hives were able to withstand nuclear Armageddon in thanks to their isolated locations and the anti magical fields that their thrones were able to produce but following after the last day the Hives quickly began fighting among each other as many Changeling hives died out due to not having any stockpiled "food" or being conquered by a greater hive but nether the less the Changeling were able to survive as a race and were able to maintain their civilization somewhat with the Hives becoming isolated city states, over the passing of the last two centuries the Changelings have become nothing more then a boogeyman with many ponies believing their existence to be nothing more then myth and fairytale to keep the little colts and fillies from misbehaving, with now and days many changelings choosing to operate in brothels as prostitutes as a quick and easy way to feed themselves.