The War At Home
During World War 2, Los Angeles experienced a massive surge in population as hundreds of thousands flooded the city to work in wartime factories or the booming film industry. African-Americans specifically emigrated in record numbers, although restrictive housing covenants kept them crammed into the increasingly segregated South Central area of the city. While Captain America fought the Nazis and HYDRA overseas, on the home front Jewish gangster Mickey Cohen tightened his grip on organized crime throughout the city, monitoring visionary but lunatic mobster Bugsy Siegel for mafia interests back East.The City of Los Angeles preferred a tightly controlled flow of vice, legalizing card, slot and bookmaking operations in limited areas of the city - particularly in areas dominated by African-Americans and other minorities. They were willing to turn more control over racial minorities to organized crime in return for tax dollars. And after the war when the wartime industries started to close up shop or return jobs to the white men they believed deserved it, times got very tight for many Angelenos.
At the same time, Los Angeles underwent a cultural renaissance, as West Coast jazz began its ascent and African-American radio began to lay the groundwork for what would become the rock and roll revolution.
The characters are crimefighters in this deeply divided time and place, championing the justice and equality America promised and fought for overseas but didn't quite bring back with it to its own shores.
If you liked L.A. Confidential or L.A. Noir but thought you might have more fun if there were with laser beams, HYDRA sleeper agents and communist robots, this is the campaign for you.
Characters
Because we know little of postwar superheroes in the Marvel Universe, there's a lot of wide open opportunities for characters in this game. The first question you have to answer is whether you want to time-shift the Marvel Universe back to 1950 or whether you want to let them remain in the future and come up with other characters. The Plot Points blog has a good description of how timeline shifting in Marvel comics works. You could simply say Captain America wasn't frozen in ice for THAT long, and make Reed Richards a rocketeering pioneer if you wanted to use feature characters in this campaign.
But I tend to look at this as an opportunity to create an all-new milieu. Maybe SHIELD is just a bunch of guys in squarejohn hats working in an office with (gasp!) electric typewriters?! Maybe Stalin really is trying to infiltrate communist supersoldiers into American society. If you decide to go with all original characters, you should also take some time to make some all-original threats.
Events
There are two forces at work in this campaign and they go hand in hand: organized crime, and racial prejudice. Racial prejudice keeps law enforcement from being able to handle organized crime. Criminals play on racial prejudice to keep communities separated and ineffective, while themselves disproportionately targeting those who have no voice to cry for help.
Events for this campaign should focus on threats that will tear the city apart: A kingpin makes a move in a mob war that sets the city ablaze, strange experiments with HYDRA technology threaten the safety of the city, but the first ones hurt have no one to speak for them, a weird alien disease begins to spread and crazed paranoiacs throw up quarantine zones.
The characters should succeed by bringing people together, by teaming up and creating Resources in Transition Scenes about coordination and community support. Emotional or mental conflicts in Action Scenes should be key.
Milestones
Milestones might involve fighting for a political change in the world, or finding out the truth about some mystery buried after the war. For veterans returning home, or Japanese-Americans released from internment camps and returning to their now-lost neighborhoods, it might involve finding someone or something left behind, or rebuilding what they used to have.
Example: 1 XP when you declare that someone you meet is someone you met while in the service or overseas. 3 XP when you seek out a secret that was buried due to the need for wartime unity. 10 XP when you expose the secret or bury it forever.