Why did that Athenian orator Demosthenes warn his fellow citizens about Philip second?

Demosthenes warned his fellow citizens about Philip II of Macedon because he saw him as a threat to the independence and freedom of Athens. Philip's expansionist ambitions and military conquests in the Greek world posed a direct threat to the city-state of Athens and its democratic principles. Demosthenes urged Athenians to unite and oppose Philip in order to protect their way of life.