In the funeral oration venerating the Athenian dead as reported by Thucydides, one of the themes is the inherent differences between Athenians and Spartans. Perikles strikes on government differences, educational differences, personality, et cetera, while praising Athens and downplaying the virtues of their opponents. One of the striking contrasts (according to the Perikles of Thucydides) is between bravery, as Perikles mentions that:
When the Spartans invade our land, they do not come by themselves, but bring all their allies with them; whereas we, when we launch an attack abroad, do the job by ourselves… (2.39)
He then goes to to describe that Athens never sends out its entire strength, so their enemies should fear that day, since they are already defeated by mere detachments.
In such a speech it stands to reason that he would praise the exploits of Athenians, exhorting and calling upon-as Admiral Nelson would later put it-‘Every man to do his duty’. To say, though, that Athens stood alone where Sparta required contributions from their empire to invade Attike is nothing more than hyperbole, as it overlooks the nature of the Athenian ‘Empire’. Even further, during the first year of the war and increasingly thereafter, Athenian allies did contribute to military expeditions.
The Delian League was set up in such a way that the allies were required to submit either a certain number of troops or a certain amount of tribute. Lesbos, Chios, Zakynthos, Kerkyra and a small handful of other states repeatedly appear providing triremes for the Athenian fleet. Those that did not contribute instead provided Athens with money to build, equip, and man up to 250 triremes on active duty at any given time. These two aspects together make it so that Athens was hardly fighting alone, even on those occasions when it was a purely Athenian fleet raiding the Peloponnesian Shores. Sparta alone could summon an imposing army, but her league did not pay tribute to Sparta, but was geared instead to march at the call of Sparta. Thus the Peloponnesian War truly was between Sparta and her Allies and the Delian League, whether or not the financial contributions, if anything encouraged, were recognized.
Second, even before the Periklean strategy of limited operations was abandoned, Athenian allies contributed forces to the allied efforts, even if they were just tokens. After his death, Athens began to campaign more widely and instead of using their own forces, would often contribute a token force, supplemented with Messenian, Elian, Mantineian, or other allied forces. In particular these were hoplites, and wherever an Athenian fleet would go, they would enlist allies to make up the bulk of the force. Exceptions to this include Demosthenes’ Boiotia strategy where his force enlisted allies, while the main Athenian army bumbled into the Thebans at Delion and lost.
In some ways the vast over-extension of Athenian resources was enabled by the allies they could call upon, whether in Akarnania, Thrace, Sicily or the Peloponnese. In the infamous Sicilian Expedition, less than a third of the hoplites sent were Athenian; while the Athenian loss of life was staggering because of the fleet losses and reinforcements sent, a mitigating factor in it all was that a relatively small porportion were actually Athenians. Not that this helped much, but it should still be noted.
True, the speech is exhorting bravery of Athenians and the courage to abandon land and homes for the city, seeking to belittle the Spartans and simultaneously paying homage to that the vast majority of the fleet was Athenian; this is even without recognizing that the power of the Athenian fleet was magnified by skill to the point that they routinely were willing to engage Peloponnesian forces twice their size. It just manages to omit one of the key factors that enabled Athens to reach and then overreach.