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Historians still debate on what drove the Athenian expedition to Sicily. Most of them including our main sources Thucydides and Xenophon point out Alcibiades and the Demos boundless ambition as well as the need from Athens to dominate western trade.

The Sicilian expedition was the brainchild of Alciviades who pushed heavily for her. Unfortunatelly for him Nicias and the traditionalist faction were able to severely limit the force that he requested [1] by reminding the Athenians the danger from the Spartans. Alcibiades was also involved in some minor scandals at the time - being a prominent pupil of Socrates- and this further damaged his position in the Assembly. His opponents even tried to blame him and his friend with the sacriligeous act of breaking the phallus of the Hermai but the case failed spectacularly in court.

So in early spring 415 a 80 triremes sailed from Athens toward Sicily. Abroad them were 4000 Hoplites and 800 Psiloi. The expedition was under the sole command of Alcibiades. The assembly had decided that a single strategos should handle all decisions. Some modern historians like to argue that given what transpired after the arrival to Sicily that the Athenians should have send a larger force although many point out that a larger force would have been far more difficult to manage and would have perhaps needed a different style of command.

Nevertheless Alcibiades decided to pursue an extremely aggressive strategy. He realized more than anyone that a prolonged campaign would only hurt Athenian interests in the region and would invite a Corinthian or Spartan counter expedition. He pursued an extremely aggressive diplomatic campaign and managed to ally with many poleis in the region. The main hurdles that he had to overcome were the Doric colonies headed by Syracuse. He knew that without the focal point of Syracuse then all the Greek cities of the region and perhaps those of Megali Hellas would join the Athenian league.

Following a year of seeking allies and bolstering his army (and even drilling the allied navies so that they were almost as good as the Athenian one) in early 414 he felt confident enough to attack Syracuse. The siege of Syracuse is one of the most famous of antiquity and perhaps without Alcibiades diligence and ingenuity it could have been a huge failure for Athens. The Athenians build a wall surrounding Syracuse and used their navy to aggressively blokade the city. In one of those minor skirmishes 5 Corinthian triremes that were coming in support of Syracuse were sunk. Abroad them was the Spartan general Gylippus [2]who was sent to help Syracuse organize its defense.

In 413 Athens sent reinforcements to Sicily. 50 triremes with 2000 additional hoplites under Demosthenes arrived outside Syracuse. This was the final nail for the Syracusians. After a year of hard siege and seeing fresh soldiers bolstering the enemy ranks they decided to surrender. It is a statement to Alcibiades political savvy that he didn't ask for very harsh terms on the Syracusians. They were to be part of the Delian league and change their constitution but overall it was a very lenient peace.

In the next year (412 BC) Alcibiades and Demosthenes toured almost all the Greek cities in Italy and with either gentle words or show of arms managed to get almost all of them in the Delian league.

The Spartans were unwilling and unable to intervene following the death of Gylippus even though the ephors realized what those changes in the west certainly affected them. The most obvious one was the decision from Corinth and Sicyon to leave the Peloponessean league since the Spartans had done nothing to support them in their colonies problems. This lead to the 412 Spartan campaing in Corinth . The Corinthians lost badly on land and they asked for Athenian support. Nicias the aging general tried to resolve the issue diplomatically. His negotiating style was vastly different from 421. For once Athens was in a clear dominant position and even the Spartans knew it. The end result was called the Niceios symfonia [3]. Corinth, Megara, Sicyon and Argos were added to the Athenian league. The other Pelloponesean cities could do as they wished but most opted to remain allies with Sparta. The cities that left the Spartan alliance thrived on western trade and following the Sicilian expedition needed to be on very good terms with Athens. Some Athenians were also opposed to the symphonia, particularly Alcibiades who felt that it undid much of what he had achieved in Sicily from an economic viewpoint.

So in 410 BCE the Athenian league was the undisputed controller of the seas in the Aegean and south Italy . Sparta had lost most of its navy (Corinth amounted for almost half the Spartan navy) even though some ephors were trying to get in contact with Persia in order to build a new navy with persian gold. Sicily and southern Italy had become a Athenian controlled zone which would bring a great deal of prosperity in the region. War in mainland Greece seemed unlikely given that Sparta and Athens had reached something akin to an understanding. Persia agents were still trying to figure why the Greeks were so quiet. Nevertheless war came to the Greek world. It came from the west with the battle cry "remember Himera"...

[1] first POD in OTL Nicias tried to warn the Athenians that the expendition was too dangerous and it would require far more than what was requested and as a result the jingoist demos voted for a far larger expedition. Also this lead to the disastrous 3 generals in command of an expedition situation
[2] Second minor POD in OTL Gylippus galvanized the Syrracusean defense and elan. ITTL he never lands.
[3] Loosely translated the agreement of Nicias
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