Aristotle opposed the views of Speusippus and he may have left the Academy following Plato's death for academic reasons or because he was not named head of the Academy. Or he may have left for political reasons before Plato died because of his unpopularity due to his Macedonian past. .
Aristotle traveled from Athens to Assos, which faces the island of Lesbos. He did not leave the Academy alone; Xenocrates of Chalcedon went with him. Aristotle married Pythais, the niece and adopted daughter of the ruler Hermias, and they had one child, a daughter who was also called Pythais. Pythais was probably only eighteen when they married, and died ten years after their marriage. On Assos, Aristotle became the leader of the group of philophers, which Hermias had gathered there. Aristotle had begun his work Politics on Assos as well as On Kingship (which is now lost). .
His time in Assos was ended by political events. The Persians attacked the town and Hermias was captured and executed. Aristotle escaped and went to the island of Lesbos on his way to Macedonia. His stop in Lesbos was more than a passing visit because he remained there for about a year and must have had a group of Scientists from Assos with him because they continued their biological researches there.
In 343 BC, Aristotle reached the Court of Macedonia and he was to remain there for seven years. It is said that he became the tutor of the young Alexander the Great, son of Phillip. The treaty between Athens and Macedonia began to fall apart in 340 BC and preparations for war began. The next year Speuippus died but Aristotle, although proposed as head of the Academy, was not elected. This position went to Xenocrates and Philip lost his support for Aristotle. In 335 BC, when Alexander became King, Aristotle returned to Athens and established his own school, the Lyceum. Because much of the discussions in his school took place while teachers and students were walking around the Lyceum grounds, Aristotle's school became known as the Pericatetic ("walking" or "strolling") school.