I don't see it as "most powerful" (what's powerful is the American army and passport). I see it rather as most useful. It is widely-spoken and it is the language of academia and pretty much the internet.
It is simply the result of various historical events - any language could have been used. Had the Aztecs colonized the world, we'd all be speaking Nahault.
English language is powerful of course, but the most powerful one I think is Chinese. It's a language of the future.
It took centuries for English to displace French so I don't think Chinese (or rather the official Mandarin) is going to be the lingua franca anytime soon.
Why argue which language is better?
There is a language of deaf-dumb people - and there it does not matter who you are or what country you are from, right?
At the moment, English is more communal throughout the world, but everything can change if our planet survives a couple of millennia ...