Hello, this is a question I asked myself for a long time because I heard from others that you can't fly on more than 25mw of video output power outside of the US, is that true? I'm new to the hobby, so the question might seem dumb, but still, answer please even if you find it obvious, because I don't!
Suggest reading a few comments down there someone shares links for how to get licensed. Basically same thing applies in the US but we can use up to 500mW transmission without personally passing a test that essentially makes sure you know what you are doing at least at a novice level when it comes to messing with radio equipment. The tests in the US aren't completely trivial but nothing an average student/person couldn't learn in a few weeks to a couple months depending on your background.
Honestly you can get pretty good range on just 25mW with good antenna and other components.