Um.

[How to go about this without giving himself away?]

I think--initially--there wasn't a lot of trust, when the superheroes started crawling out of the woodwork. So they got used to doing things on their own. And then they started working together, and got used to doing it without having to answer to any particular government--the teams go all over the world, rather than staying in one place. The Justice League is based in space these days.