Because they hoped to share in the spoils of a conquered Athens.
Because Athens had enslaved all her other allies.
Because they were afraid the Athenians would lose the war.
Because the Spartans were willing to bribe them to switch sides.
Because during the Persian War, they had fought with the Spartans against the Persians and the Thebans had fought against the Spartans.
Because executing them would have been a violation of the Geneva Convention.
Because Athens would seek vengeance for their deaths.
Because they had been of service to the Spartans during the war.
The love of money
To forestall a rebellion at Leontini
To prevent corn from being exported to the Peloponnesus.
To obtain more lumber in order to build more ships.
To test the possibility of conquering Sicily
Their lightly armed javelinists were able to prevent the hoplites from closing with them.
They bribed the Athenians' Messenian guide to lead them into an ambush.
They significantly outnumbered the Athenians.
Demonsthenes was an inept general.
He made use of the mobile tactics previously used against him by the Aetolians.
His pre-battle speech so inspired the Athenians that they overwhelmed the Ambraciots on the Peloponnesian left.
He set up an ambush that hit the enemy's left wing from behind once they were engaged.
He built a very large line of forts and trenches that forced the Peloponnesians to attack him in a strong defensive position.
A strange star appeared in the skies for many nights.
Mount Etna erupted.
An asteroid struck the Acropolis.
A tidal wave struck the western coast of the Peloponnesus.