Triscuits

IR undergraduate rankings for Brazil are quite debatable, and USP leads the last one. In General USP and Rio Unis have the best brand value overseas. Nonetheless, Federal Universities are well-regarded. You should get a letter of recommendation from Paulo Visentini, he was Rio Branco Chair at Oxford recently. Reis da Silva has taught at SOAS and did his PhD at Leiden which is well-ranked.

Just a quick question, since application season is now underway. My grades were meh in my three undergraduate years. Then I improved and my Master's dissertation was summa cum laude (overall degree: magna cum laude). Is a sharp improvement over time good, irrelevant, or bad (admissions committees look for anything to eliminate you, I guess)?

The University of São Paulo is well regarded for South American applicants, that's where you graduated from ?

Well, just look at the affiliations of those who publish in the Hague Journal of Diplomacy. But you don't need an advisor that's a specialist, by the end of the PhD you'll know more than him anyways.