Complex sentence: On their return both generals were unsuccessfully accused of having retained their command beyond the legal term, but the fact is that the democrats and also some aristocrats of Thebes aknowledged Pelopidas and Epaminondas were the two most capable and important personalities of their city.
Split into simpler sentences: On their return, both generals were accused, unsuccessfully, of having retained their command beyond the legal term. In fact, the democrats and some aristocrats of Thebes acknowledged that Pelopidas and Epaminondas were the two most capable and important personalities of their city.