The US still is by far the most powerful country on the planet,
I wont even say is that powerfull. The Us and Europe have an annual deficit (each!) with China for over 200,000 million dollars.
The only way they still rule the world (by far) is military, but Im afraid that will change soon, its a matter of time I think, since China is more powerful economically (and they have 4 times more population.... just picture them making weapons like the US in WWII, working day and night).
Culturally the US are in total decadence (but still has some power, like making every single cable tv on Latin America and Europe to have their channels). But there are big counter culture against the US all over the world...
Politically, they have lost some power, but they still have a lot. They dont control the world as in the 90s, but they have big political actors with huge weight in every national scenario, in Latin America, in Africa and of course in Europe. US embassies around the globe still operate and can change national scenarios, like they are doing in Colombia, like they do in Europe right now...
Anyway, apart the Mercosur, Unasur and Celac, Latin America has a new card to play, which is China. That gives the continent some liberty, some posibilities, also the Sur-Sur axis, commerce with South Africa, Angola. It has a great future.
Clearly we are in a transition, like happened in the 20s with the UK and the US. Hope this wont end in another war.