Why did Alexander the Great manage to unite all of Greece?

After the death of Philip II, the Greeks decided to take the chance and become independent. However, very soon Alexander the Great advanced to Thessaly, where he confirmed his power, and then he advanced to Central Greece, where he set up camp near Thebes. At the same time, the Greeks did not expect such a turn of events. In this connection, they sent ambassadors to Alexander and swore allegiance. Thus, Alexander now became the ruler of all Greece.