This idea is based on the old
Stanley Weinbaum story
Shifting Seas. In the Weinbaum story, a large section of Central America collapses in a day. As that would create monster tsunamis and radically alter this setting, I'll go for Northern Panama, Costa Rica, Nicaragua, El Salvador, and most of Honduras, subsiding into the seas over the years 1916 to 1927.
As in Weinbaum's story, the Gulf Stream is totally warped causing serious
Climate change. Europe now has the climate of Canada at the same latitudes.
As in Weinbaum's story, this leads to war, unlike Weinbaum's story, no one can build a wall to undo the problem.
The local year is 1928, the Anglo-French fleet has brought large armies into Canada. The US army is preparing to defend itself from the alliance of Britain, France, and Germany. Meanwhile, since the climate shift seems to have made North Africa wetter, French, Spanish, and Italian, armies are leading in a mass migration of Europeans to North Africa. The Arabs are furious and desperate. The Papacy has moved to Malta. Europeans are fleeing the new ice age and the world is at war.
This Q6 world is getting some aid from Homeline, they're trying to see if, as in the story, a seawall could save the day. Centrum hopes to gain control in the crisis, or at least get rid of democracy and any form of non-European nationalist movement. The Cabal seems to find the apocalyptic mood of this world great for starting cults. But it could be more than that.