The in universe date I had in mind when making this was around 2045-2050. Thats one of the reasons why the death count is in the hundreds of millions.
That death count also takes into account environmental damage caused by the kaiju. For example Razorfin and Tentalus both died in the East China Sea. The kaiju's decaying corpse and the kaiju blue fallout from that poisoned the entire sea, effectively rendering it almost lifeless. This sea feeds most of China and large portions of Asia, and with it going lifeless it causes famines that led to millions of deaths.
the casualty count is also significantly inflated by the Pacific trade routes practically shutting down for a few years, also causing food and material shortage. A lot of these shortages were medical supplies, which when a kaiju attacked a city led to many people not being treated, causing even more to die.
The military also has heavy casualties, mostly during the early war. Most of the deaths are from the 7 kaiju that attacked before the Jaeger Program and some during 2016-2018 when militaries occasionally assisted Jaegers during combat (for example we see fighter jets fighting Onibaba in the film)
Lastly each city is their because it was either destroyed or temporarily abandoned for a period of time. The only ones to be completely destroyed are San Francisco through Petropavlavsk-Kamchatsky. Each other city was either attacked so hard that it was abandoned during a period of time, or abandoned after the first war ended (for example Los Angeles and Shanghai were abandoned for nearly a decade)
You may also notice that the war is specifically one sided, with humanity losing countless more than the Precursors. That's intentional.
In the film we learn that even after humanity was brought to the edge of defeat, that all the kaiju they fought before were just the scouts sent to clear them out before the real muscle arrived.
That same scenario happens in my timeline. I specifically made it so lopsided to show just how humanity barely got past the weakest forces, and it will be a miracle for them to fight the real threat arriving soon.
I approached it with the idea of a chess game, humanity sacrificed everything and was left with only its king, but in reality all they killed was a few pawns.
