This alternative timeline has as a major POD a union of the Greek city-states after the Greco-Persian Wars. Instead of starting to militarize, Athens join forces with Sparta, and make all cities of Greece join the Confederacy of Greece.
Confederation and Republic
The Greeks had just won the Greek-Persian wars and were in extreme conditions. Seeing the spartan war potential as useful tool instead of a powerful enemy, Athens and Sparta allies themselves, giving Greece a time of union. While Athens is chosen as capital of the confederacy, the Spartans receive a majority in the new senate, the supreme rule of the united republic. Since Athens and Sparta were the potentates of Greece, soon all of the nation was unified under the Confederacy of Greece.
War against Macedonia
Since Greece was united and as powerful as it could be, the Macedonian invasion was stopped and Greece even advanced inside the nation. Alexander and his mother had fled to Sparta, attempting to assume a military position in the Confederacy, instead of dying with his father.
Alexander soon reached a good position in the spartan army and was called by the senate to deal with the growing threat of Persia. His conquest in Anatolia allowed him to become the main general of the confederation army. After the conquest of Anatolia, the senate ordered Alexander to invade Israel, instead of advancing into Mesopotamia. The Greek armies reached the Sinai, and were watched by the Egyptians. Rather than fighting the Greeks, Egypt surrendered before a war even started. Soon after Alexander is called to protect Athens and train new generals, effectively stopping his military career, but yet remaining as the most important general of the republic.
Proclamation of the Republic and invasion of Carthage
The senate proclaimed the United Republic of Greece (ΗΔΕ), but rather than having a peaceful time, Greece was attacked by Carthage in Egypt and war was proclaimed. The army quickly advanced through Africa and Carthage were close to fall; instead of invading the city, the army decided to conquer any other city of Carthage and they did. Two-thirds of Sicily was under Greek control, while the republic had territories in Italy, Spain and across North Africa.
Invasion of Rome
Rome was a powerful threat to the plans of Greece. Its military tactics were even better then the Greek old fashioned phalanx, but in numbers the republic were far better with Greeks, Egyptians, Carthaginians, Israelis and more. The massive invasion of Italy by both north and south made a terrible defeat of Rome. The last stand of Julius Caesar made the invasion of Rome a Pyrrhic victory. The city was conquered, its tactics were possessed and so, the Greek military was unmatched.
Conquest of West Europe
With the powerful military, the Gauls and other French-Spanish tribes fell to the Greek might. The colonization process was slow but effective. The Greek language was expanded through Greek Europe, and all of the "barbarians" outside it were in terrible fear of the Greek might.
The mighty Greek senate had lost its prestige and several generals wished to gain power and become emperor.
First Civil WarThe republic were in peace, colonization of Great-Britain and Ireland started and most of the nation focus were there. The military were stationed in mainland, and several generals were tempted to take power from the senate. Nikolai, the commander of the Republican Guard, relative of Alexander, proclaimed the senate dissolved and that new elections were to be held. Athens guard revolted and proclaimed the former senator and general Pericles IV, relative of Pericles, the ruler of Greece. The republican guard and the Spartan guard proclaimed Nikolai the ruler of Greece. A mediator was elected to resolve the situation, but he was murdered by a roman nationalist. Both generals were accusing the other of the murder and so the war started. Most of the members of the republic supported Nikolai because of his heritage of Alexander abilities.
With good farming provinces and several ports of major commercial importance, the funding of Nikolai army was easy, and his position across the people helped him a lot.