After the Peloponnesian War, the poleis were weak. Philip, the king of Macedonia located in the north of Greece, declared war on Greece and conquered almost all the Balkan Peninsula.
Alexander the Great, Philip´s son, continued the territorial expansion conquering Egypt, Asia Minor and Persia reaching India.
This period is called the Hellenistic Age as the Greeks called themselves Hellenes, and because Alexander was based in Greece. The territories conquered by Alexander were known as the Hellenistic kingdoms. This period was very important since Greek culture mixed up with Persian, Egyptian and Asian cultures and many scientific advances were made as well as new philosophic ideas were developed.
After Alexander´s death, his generals divided the empire into provinces called Hellenistic Kingdoms. Trade grew and Greek culture expanded in these territories. Around 30 BC all these kingdoms were conquered by Rome and they belonged to the Roman Empire.
Alexander the Great Skeleton Notes