Before discussing, or even considering, the possibility of the "next world leader", we should probably make sure that we agree such a person/country actually exists at present. I personally do not agree.
History has seen "world bullies" often, but I doubt there has ever been a such a figure as a "world leader". I see the States as the hugest bully of this era, but that is about all. I cannot find in the States -or its governments- anything that might make me see that country as a leader. Anyway, to answer the question "who do you think the next world leader will be?", I will say "hopefully, no one. Let each community have the leader they think is right for them; let each community handle their affais in their own way."
Leandro, you are living in Mar del Plata at the moment? I live in MdP as well. Are you a student of English? A teacher? I'm curious. Perhaps we know each other? In any case, it's great to see someone else from my city here!
Miriam