In 337-336 BC Philip divorced Olympias, declared war on Persia, and was assassinated. Alexander was then 20 and immediately declared the new king of Macedonia. From the very beginning he established his authority by executing all persons alleged with his fathers assassination as well as all possible rivals and factions that opposed him. Alexander was then confirmed as strategos autocrator (supreme commander).
In 335 BC Alexander began blitz campaigns against the Triballiand Ilyrians. He then marched into Thrace and defeated the Triballi, crossed the Danube and brought the Getae and Celtic tribes under his control. Abruptly after he defeated a coaliton of Illyrians who invaded Macedonia.
The Greeks growing weary under the rule of Macedonia and hearing rumors about Alexander's death in Illyria revolted. Due to this Alexander marched his armies 380 kilometers in 14 days ordering the Thebans to surrender. When they refused he marched into their city and destroyed it sparing only temples and the poet Pindar's house. 6,000 were killed and the survivors (30,000) were sold into slavery for 440 talents of silv