Complex sentence: Suddenly unable to guarantee their own security, the Athenians were forced instead into making peace with Philip; the treaty that was agreed (the Peace of Philocrates) also made Athens reluctant allies of Macedon.
Split into simpler sentences: Suddenly unable to guarantee their own security, the Athenians were forced instead into making peace with Philip. Their peace treaty, known as the Peace of Philocrates, made Athens reluctant allies of Macedon.