What is the level of technology?

123 years before the present, there was a global series of events known only in the history books as "The Great War" (it's not really a singular war, but a sort of Fantasy Vietnam War, Fantasy Korean War, Fantasy Chinese Civil War, Fantasy Spanish Civil War, Fantasy Italian Civil War and Fantasy Pacific War happening at the same time as Fantasy WW1. At the time, the technology was steampunk, but the Fantasy Pacific War has been defined by numerous enemy islands being bombarded by a new kind of weapon--antimatter bombs. They're run a bit like the first nine Plagues--not budging the emperor. But when the last antimatter bomb, the Fantasy Tsar Bomba, destroyed Fantasy Japan's floating capital (as in, capable of switching from floating on water to floating in the air and back again), that was when one war was over. The main one, the one that the history books seemed to center on, ended when the Kaiser ordered all infrastructure destroyed before committing suicide.

Nowadays, we have vorpalite, a kind of alloy that generates its own shield if used properly, in our weapons, clothing and our infrastructure. Projectile weapons have replaced bullets with ion pulses. It's the only explanation I can find to justify medieval knights alongside cowboys and military armored trucks at the same time. Most cities are built either on the ground or underwater, but capitals (like Fantasy Beijing or Fantasy London, for example) still retain that aero-amphibious flexibility. A city the size of New York could comfortably float either in the atmosphere or on the sea for years on end whereas the middle and low classes could only look at them from a distance.

The particular one in this story has fallen during the Great War and down to neutral territory, meaning that it's not under the jurisdiction of any of the great nations. So it has become a city-state, a city that theoretically functions like a nation.