Try this idea...
In superhero comic books, villains are always threatening to destroy the world or at least mess it up badly. How likely is it they'd never succeed?
Just a few years after the new age of Super Heroes is started, (I'll use DC I know it better),
Vandal Savage and
Per Degaton launch an attack on the world. They restore the conditions of the
Older Dryas weathing the world in ice. Well the new Justice Society smashes their gang. But the Villains manage to trap the Specter and themselves in an alternate dimension, a universe without time. Before any of the heroes can act, Per Degaton's machine fuses out into a pool of molten metal. The world is locked in a new Ice Age.
It's now the year 1960. California, the American Southwest, Florida, and Hawaii are the main centers of what is left of the USA. The surviving Canadians moved south and joined the USA. Except for Southern Texas, most of the rest of the USA is tundra.
The Government of France Outre Mere Rules North Africa west of Egypt. The area now has regular rains and is a fertile grassland. The collapse of the Central Asian Summer High Pressure System ended the Indian Ocean
Monsoon System turning India, Burma, Thailand and Vietnam into deserts.
A cooler rainier Australia wasn't doing well with its agriculture, but
Rex Tyler led an effort to develop new types of fertilizer and new systems of fertilization and made Australia the planetary grain basket.
Most of the surviving populations of Europe that didn't go to North Africa went to Latin America. The Japanese and Koreans, desperate for survival fled either to Latin America or the Philippines.
Hitler marched the Germany armies into Russia to crush the Red Army. No news came back from the east, only the howling of the icy winds. What Germans could, fled Germany as they would a vampire's tomb.
After years of poverty and chaos the world is beginning to heal. Trade and industry are beginning to perform in normal ways. The USA is still a Democracy.
Dr. Fate healed FDR to make sure America had a leader for the crisis, not believing it would be permanent. FDR lead the nation until 1956 when he was finally allowed to step down. America is a Democratic Socialist State with a strong market sector.
The British Empire has multiple restrictions on the franchise, but a higher proportion of the people of the Empire can vote than English men in
1860. The rights and needs of working people are better respected than they were in 1920's England and civil liberties are better than they were in Homeline's UK in 1990.
Most of Latin America is some kind or other of an Oligarchy. Africa is mainly colonized with only Liberia and Ethiopia independent. Liberia is a functioning democracy with problems they are working on productively. Ethiopia is an fairly archaic Empire and claim to prefer going their own way. The Philippines is an Oligarchic Republic but far better off than it was in Homeline's 1960's.
This is a low manna world with small areas of Very High Manna. The Tech level is seven with super technology. The main source of supertech is
Ted Knight's Cosmic Ray Rods. They supply almost all of the electric power, and everything that can be is electrified, and also powers most vehicles. There are also sea surface cities across most of the pacific. These are American installations built to house refugees during the crisis, and have since become spacious and comfortable. They are now working on being beautiful as well.
Per Degaton's machine not only brought back ice age climate conditions but also many ice age animals. Some of these animals are amazingly deadly.
The world is still in turmoil. Supers are still most common in America but they are all over the world now. Hitler and Stalin may have gone missing for nearly two decades but their ideas appeal to many people around the globe, some of these are supers in their own right. The would be heirs of the dictators seek to rule the world. Can you stop them?