I think instead of spelling out everything, having the characters introduce the world might be helpful. The first essay is written by the character Dustin Wheelin, the current Liberteen. It is purposefully poorly written but there is some important backstory there about the American Justice Squad.

Superhero History From 1950 – 1960.
An Essay by Dustin Wheelin

The first superhero arrived in 1950. His name was Mister Fearless. He possessed the ability to project his own fears in the eyes of his opponents. He ended up dying after his second year in office of being a superhero.
After that point the first Capitalist showed up. With his powers of earth control and ability to deal well with people, he became a popular hero and formed the first American Justice Squad. It was very helpful and was formed in 1952.
The first heros to join were AmeriMan, Habadasher and Apple Fly. For no reason other than branding superheroes started using puns in their names. They still do it and it is stupid.
The early enemies were mostly scientists trying to find out why these powers were developing. They also stopped crimes and Nazis.
In 1956 AmeriMan was brutally shot down by police who mistook him for a burglar. As a result, the twins Penance and Sworder proposed a national law that would give superheroes in the United States more freedom. With the power of AmeriMan’s death, the Capitalist easily passed the law in 1957.
The law allowed superheroes to use their own jurisdiction in apprehending and dealing with crime. The laws are secret and only known by members of the American Justice Squad. All attempts to remove the laws have been met with disaster.
In 1958 the first war of the supermen happened when British hero Winston Torchkill faced off with The Capitalist over the issue of Indian democracy. The battle had both people die in it and the first Liberteen took over the role of the Capitalist. The British Empire was then forcibly disbanded.
In 1959 the first superhero was stripped of his protection and was forcibly executed and removed from all records except to say that he was removed.
Superheroes do a lot of good for our country and are very important.