Philip II, King of Macedon from 359 B.C-336 B.C, was assassinated by his bodyguards on 336 B.C. Philip II's successor was Alexander III.
However, Alexander was a bit young and the Greek city-states and the Thracian tribes, whom Philip defeated, rose up in revolt, attempting to expel Macedon domination in Greece. However, Alexander cruelly defeated the Greek troops and razed Thebes, one of the main Greek combatants. Athens was spared from sacking.
The next target of Alexander was Thessaly, another Greek combatant that rebelled against him. Alexander saw that they're occupying a mountain pass that blocks on his way so he dispatched a cavalry unit of 3,000 men to find an alternative route. They found an alternative and Alexander went to the Thessalian rear. When the Thessalian soldiers awoke and found out that Alexander was in their rear, the Thessalians immediately surrendered.
Alexander continued to campaign in Europe, defeating the Thracian and Illyrian tribes and also Greek cities that rebelled against him. However, after Alexander sacked Thebes, most Greek cities submitted to him, accepting Macedon domination.