At the beginning of Alexander of Macedon's campaign to conquer the Achaemid Empire, he died.
Alexander of Macedonia had unified Greece and wanted to conquer some land. He was at the front line with a distinctive helmet. The Persians knew it and surrounded the front line. Spithrade, a Persian army official, struck Alexander at the skull. This axe fell true (POD) and killed him.
Fall of League of All Greeks
The League of All Greeks collapsed. The restored city-states would be weak, not knowing what they lost with Alexander's death. However, the one city-state that did not become part of the League of All Greeks, Sparta, would continue to be powerful.
Carthage saw this occur and decided to take use of this opportunity. They colonized the west coast of Italy. However, this would put them at odds with Rome (a great power at the time.)
Carthage invaded Latium and, with little resistance, occupied it in 327 BC.
Sparta would take the east coast of Italy. Italy would act as a power keg amongst Carthage and Sparta.
Spartan Punic Wars
Eventually a battalion of Spartan soldiers crossed into Punic Italy. This minor act started war between Sparta and Carthage. This war would prove inconclusive and would last for a long time, incapacitating Carthage and Sparta.
The Achaemenid Empire, after defeating Greece, collapsed at around 323 BC. They were already about to collapse and in their wake several small kingdoms were created
Carthage would also collapse at around 320 BC, due to stress with their war with Sparta. The Etruscans and the rest of the peoples of the Italian Peninsula would become independent as well (Latins, etc.)
Sparta would collapse as well at around 317 BC, resulting in no powers existing in Europe as the Archaic Dark Ages began.