Pericles' initial strategy could well be called the rope-a-dope maneuver. The Athenian army was no match for the Sparta-led forces, but those forces, in turn, were not powerful enough to assault Athens directly. So Pericles evacuated the countryside, brought everyone within the city walls, and allowed the Spartans to lay waste to the surrounding country. He, in turn, sailed the Athenian fleet down to the Peloponnese to lay waste to the countryside there. Each spring the Spartans would march out and the Athenians sail out. Each would lay waste to the other's countryside and then go home before winter set in. Neither could conquer the other in this way. The Athenians lacked the land power to march any distance inland, and Sparta was fertile enough not to be vulnerable to blockade. Athens, in the meantime, imported most of its food, but had unassailable Long Walls to its port and was also invulnerable to blockade so long as it ruled the seas.
The city walls kept out invading armies, but they were powerless against the "invisible armies" that so often accompany war. Bringing all the country people into Athens created crowded, squalid conditions and soon led to a plague and general breakdown in morale. The Athenians sought to negotiate a peace but did not receive any satisfactory offer. The Athenians turned against Pericles, but ultimately did not more that assess a fine against him, and reelected him shortly afterward. Not long afterward, Pericles also came down with the plague and died, about two and a half years into the war.
The plague did not prevent the Athenians from continuing their siege of Potidea ultimately starving it into submission (430-429 BC). The Potideans were forced to leave with no more than a single garment for men and two for women and a fixed sum of money, to take refuge with neighboring cities. One can only assume that this increased hatred of the Athenians in the Chalcidice. The plague may have kept the Athenians from coming to the aid of beleaguered Platea when the Peloponnesians joined the Thebans in laying siege to it (429 BC). Nor did the plague stop the Athenians from winning naval victories. Even when outnumbered, their superior skill triumphed over the inexperienced Peloponnesians.
revolted. Lesbos had more autonomy than most Athenian allies -- it contributed ships and sailors to the alliance instead of paying tribute and was allowed to run its own government as it pleased, and it pleased an oligarchy. The most probable reason for the revolt was that Mytilene, the largest city on the island, wanted to be local hegemon and the Athenians disagreed. The democratic city of Mythemna (also on Lesbos) resisted Mytilene hegemony and called on Athens for help. The Mytilenes called on Sparta to protect them from the bigger hegemon of Athens. (This is one of many examples showing how pointless it is to try to sort out good guys from bad guys). The Athenians blockaded Mytilene to starve it into submission (the usual tactic of a naval power conducting a siege). The Spartans slipped a general into Mytilene and, despite their recent naval defeat, sent a fleet to Mytilene's relief. But the fleet took its time. In the meantime, the Spartan general, desperate provided heavy arms to the common people. The people promptly demanded an equal share of the city's dwindling rations or they would revolt and make their own peace. The authorities then surrendered, the only condition being that they would not be harmed until the Athenian Assembly decided their fate. The Athenian general sent the Spartan general and the leaders of the revolt to Athens. Meanwhile, the Spartan fleet had taken its time, but eventually crossed the Aegean, only to learn that it was too late. The fleet commander passed up an opportunity to stir up a revolt, and alienated some potential allies by taking unwary visitors prisoner and executing them. Then, upon hearing that two elite Athenian ships were in the area looking for the Spartans, they turned and fled.
Despite the Spartan fleet's underwhelming performance, the Athenians were alarmed that their enemies had proven themselves capable of crossing the Aegean. It did not bode well for the future. In their fear and alarm the Athenians had the Spartan general executed, despite his promises to lift the siege of Platea if he were spared. They then voted to kill all the Mytilenian men and sell the women and children as slaves, in the theory that only the most extreme measures would deter future revolts. The next day, though, the Assembly relented, persuaded by the argument that (1) a more merciful policy would encourage hostile cities to surrender, and (2) the democratic element everywhere was a natural ally, unless the Athenians alienated them by such indiscriminate slaughter. These arguments narrowly won the day. But the Athenians still treated this rebellious ally with unprecedented severity. They executed the "ring leaders" sent to Athens, 1,000 in all (probably the entire Mytilene oligarchic party) and turned all the land on Lesbos over the Athenian owners, with the local population as tenants.** If this was "mercy," then things had fallen very far indeed.
As for the Spartan general who offered to lift the siege of Platea if he were spared, it soon became clear that the Athenians should have accepted his offer. Shortly afterward, the Plateans surrendered on the assurance that they would be treated fairly. Instead the Spartans, urged on by the Thebans still angry at the Plateans for having killed captured Thebans, executed all the men for the "crime" of opposing Sparta in the war. The remaining women were sold as slaves and the city destroyed. Thucydides attributes the Spartans' severity to their desire to stay on good terms with Thebes. But it seems likely that the Spartans were also angry over the execution of their general and ready to take it out on whoever was closest at hand. Presumably if he were alive and in Athenian hands, the Spartans would have restrained their Theban allies so they could trade the Plateans for their general. Two other points should be made about the massacre as Platea. First, bad as it was, it was simply not on the scale of what the Athenians has proposed in Mytilene. Mytilene was the largest city in Lesbos. Platea was tiny. The Athenians had evacuated most of the non-combatants, and about half of the combatants had escaped, while the women sold as slaves may well have been slaves from the start. Second, the Athenians were not blameless here either. Before beginning the siege, the Spartans proposed that the Plateans leave their city and it would be returned to then after the war. The Plateans refused upon Athenian assurances of protection. The Athenians should have kept their promises if they were able, or not made them in the first place.
*How long is "very long"? I would classify of war of six months or less as short, of six months to two years as fairly short, of three to six years as medium, of more than six years as long, and more then twelve or fifteen years (not sure where to draw the line) as very long.
**Some (presumably pro-Athenians) commentators believe that the number is in error and that the actual figure was much smaller. They also suggest that Mytilene oligarchs owned all the land anyhow, so the people were just swapping one set of overlords for another. But presumably given the choice, the Mytilenians would prefer local to foreign overlords.