Alexander the Great
When Alexander, the oldest son of Philip, King of Macedon, was born in 356 BC, the greatest empire in the world was the Persian Empire. The great Persian conqueror Cyrus had conquered lots of smaller countries to put together the Persian Empire more than a hundred years earlier. Macedon was a small kingdom on the edge of the Persian Empire.
Alexander's father Philip was a strong and ambitious king. He wanted more power than just his own little kingdom of Macedon. Philip spent most of his life conquering the cities of Greece, to his south. By the time Alexander was eighteen years old, he led the left wing of his father's army at Chaeronea, the last big battle to conquer Greece.
Alexander fights Darius at Issus (mosaic from Pompeii)
Two years later, when Alexander was twenty years old, a guardsman killed his father, Philip, and Alexander became king of Macedon and Greece. Soon Alexander decided to be like his heroes Cyrus and Achilles and conquer the Persian Empire for himself. In 335 BC, Alexander crossed over the Hellespont into the Persian Empire, marching his army south along the Mediterranean coast towards Egypt, conquering all the cities along his way (most cities actually just surrendered when they saw him coming).
After Alexander conquered Egypt, he finally met and defeated the Persian king Darius III in battle at the battle of Issus in 333 BC. Darius ran away, and Alexander continued on through Mesopotamia (modern Iraq) into Persia itself (modern Iran).
To find out more about Hellenistic Greece, check out these books from Amazon.com or from your local library:
Oxford First Ancient History, by Roy Burrell and Peter Connolly (1997). Lively interviews and pictures make the ancient Mediterranean come to life. For middle schoolers.
Alexander the Great, by Samuel Willard Crompton (2003). For teenagers.
Alexander the Great, by Robin Lane Fox (reprinted 1994). Lane Fox is a good writer.
The Hellenistic World and the Coming of Rome, by Erich S. Gruen (1984).
The Greek World After Alexander, 323-30 BC, by Graham Shipley (2000). Takes a more positive view of the Hellenistic period than Gruen, but it's not as entertaining to read.