With Egypt and Macedonia weakened, the Seleucid Empire made increasingly aggressive and successful attempts to conquer the entire Greek world. Now not only Rome's allies against Philip, but even Philip himself, sought a Roman alliance against the Seleucids. The situation was made worse by the fact that Hannibal was now a chief military advisor to the Seleucid emperor, and the two were believed to be planning an outright conquest not just of Greece, but of Rome itself. The Seleucids were much stronger than the Macedonians had ever been, because they controlled much of the former Persian Empire, and by now had almost entirely reassembled Alexander the Great's former empire.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): Which empire currently controlled the majority of the former Persian Empire?
Seleucids