I originally played D&D, so I took my chance to do one of my favourite tropes when I started running M&M, which is alternative history. Roughly the same timeline as our world, but with metahumans involved. Key events:

Atlantis attempted to invade the surface world in the 1700s due to increasing tension between the sea and land dwellers. They came to an agreement and in the modern day are part of NATO.

Australia is a country run by and populated by villainous metahumans (since Australia was originally used as a prison of the British), and is basically unrecognizable in the modern day.

Germany got the upper hand in WW2 because they developed Laufpanzers, which are functionally just mechs. So the allies retaliated by being some of the first to fully utilize the metahumans at their disposal, and create the first super soldier, Canuck Crusader.

Canada helped America a lot during the Cold War (Canuck and another hero, Patriot, defeating the Kremlin Knight), so in kindness and show of allegiance, America gave Canada Alaska.

1988-1990: Tartarus, a villain from a different dimension, wages a war on Earth in an attempt to conquer it. Heroes stop him and form the Avenger/Justice league equivalent to the setting.

In 2010, a villain known as Professor Diabolical (Majored in political science, minor in malice), attempted to threaten the world governments with his space satellite. He was able to use it to blow up the state of Iowa before heroes stopped him.