The U.S. empire is headed for a cliff. Maybe it will even collapse within our lifetimes. But that collapse likely won't be the end of capitalism as a system; it has survived the collapse/diminishing of other hegemonic powers before. But what would the next hegemonic power even be? The EU? Russia? Japan?
I want to believe that the U.S. is the last stop on Mr. Capital's Wild Ride, but that seems naive.
Cough cough Iran cough
Brazil is strong, but more in the way of not needing to listen to anyone else than actively having power. Between the Andees and the Amazon, they're kind of isolated from their neighbors.
I don't think Indonesia has done much of anything. It could be a regional power, but China's already filled that void and isn't leaving anytime soon. They'd lose any competition with China, so they don't seem to try.
Turkey is trying, just not that well. They've occupied exactly as much of Syria is Russia allowd them to. A lot of their support for foreign groups has been religiously motivated, but if Erdogan and his brand of Islamism/nationalism fall from favour, all that geopolitical activity would stop. Qatar's probably more influential and has more of a future in regional geopolitics. Still not doing as bad as Saudi Arabia.