Title: Amphimachus of Mycenae
Content: When Electryon reigned over Mycenae, the sons of Pterelaus came with some Taphians and claimed the kingdom of Mestor, their maternal grandfather, and as Electryon paid no heed to the claim, they drove away his kine; and when the sons of Electryon stood on their defence, they challenged and slew each other. But of the sons of Electryon there survived Licymnius, who was still young; and of the sons of Pterelaus there survived Everes, who guarded the ships. Those of the Taphians who escaped sailed away, taking with them the cattle they had lifted, and entrusted them to Polyxenus, king of the Eleans; but Amphitryon ransomed them from Polyxenus and brought them to Mycenae. Wishing to avenge his sons' death, Electryon purposed to make 
Title: Seven against Thebes
Content:  their war on Thebes. The Mycenaeans agreed to join the expedition, and began assembling an army. But they changed their minds when Zeus sent ill omens. Agamemnon also says that&mdash;when Tydeus and Polynices left Mycenae, "and were with deep reeds, that coucheth in the grass" (i.e. had reached the Asopos River in Boetia)&mdash;Tydeus was sent alone on an embassy to Thebes. There he found the Thebans feasting at the palace of Eteocles. Tydeus challenged all of them to "feats of strength" and was easily victorious in every one, "such a helper was Athene to him." The Thebans were so angry that they sent fifty men, led by 
Title: Fortifications of Mycenae
Content:  Mycenae is a city in the Argolid, in the Peloponnese peninsula of Greece. It was first excavated by Heinrich and Sophia Schliemann in the 1870s and is believed to have flourished in the Mid- to Late Bronze Age. The fortifications of Mycenae were built with the use of Cyclopean masonry. With the citadel built on a cliff, the architects created protection not only for the upper class that lived within the walls, but the lower-class farmers in the surrounding areas, who could find refuge there in times of war. Due to high competition in the Mid to Late Bronze Age, the citadel wall expanded significantly with the inclusion of Grave Circle A and the addition of the Lion Gate.
Title: First Messenian War
Content:  Not wanting to experience another such battle, the Messenians fell back to the heavily fortified Mount Ithome. This is when the Messenians first sent for help from the Oracle at Delphi. They were told that a sacrifice of a royal virgin was the key to their success and the daughter of Aristodemus, a Messenian hero, was chosen for the sacrifice. Upon hearing of this, the Spartans held off from attacking Ithome for several years, before finally making a long march under their kings and killing the Messenian leader. Aristodemus was made the new Messenian king and led an offensive, meeting the enemy and driving them back into their own territory.
Title: Mycenae
Content:  The people of Mycenae had received advice from an oracle that they should choose a new king from among the Pelopids. The two contenders were Atreus and his brother, Thyestes. The latter was chosen at first. At this moment nature intervened and the sun appeared to reverse direction by setting in the east. Atreus argued that because the sun had reversed its path, the election of Thyestes should be reversed. The argument was heeded, and Atreus became king. His first move was to pursue Thyestes and all his family – that is, his own kin – but Thyestes managed to escape from Mycenae.  In legend, Atreus had two sons, Agamemnon and Menelaus, the Atreids. Aegisthus, the son of Thyestes, killed Atreus and restored Thyestes to the throne. With the help of King Tyndareus of Sparta, the Atreids drove Thyestes again into exile. Tyndareus had two ill-starred daughters, Helen and Clytemnestra, whom Menelaus and Agamemnon married, respectively. Agamemnon inherited Mycenae and Menelaus became king of Sparta. 
Title: Mycenae
Content:  and the Greek fleet departed. Legend tells us that the long and arduous Trojan War, although nominally a Greek victory, brought anarchy, piracy, and ruin; already before the Greek fleet set sail for Troy, the conflict had divided the gods as well, and this contributed to curses and acts of vengeance following many of the Greek heroes. After the war Agamemnon returned to Mycenae and was greeted royally with a red carpet rolled out for him. Shortly thereafter, he was slain by Clytemnestra, who hated him bitterly for having ordered the sacrifice of their daughter Iphigenia in order to gain favorable 
Title: Messene Redeemed
Content:  swollen stream. Eira is doomed. Hearing this, Aristomenes arranges a truce. He leads out the survivors, singing the Song of Exile. They head westwards towards Phigaleia (c.668 BC). Bringing the narrative down to the present, the Old Reciter sings of the founding of New Messene at Zankle in Sicily (c.664 BC), the long years of exile, their priest's dream of Hermes, saying Zeus has willed the Messenians' return. The Young Reciter then rushes in, excited, with news of the Thebans' victory under Epaminondas over the Spartans at Leuctra (371 BC), and of Epaminondas's recalling the exiled Messenians to their ancestral home.
Title: Onomacles
Content:  A battle was fought against Milesians supported by soldiers of Chalcideus and Tissaphernes, afterwards Onomacles and his two allies continued in preparation for besiege of Miletus. This plan was thwarted by the arrival of a Peloponnesian and Sicilian fleet, and the three allies instead sailed away to Samos, after receiving advice from Phrynichus. Not long after, and within the same year, when the Athenians at Samos had been reinforced, Onomacles was dispatched with part of the armament, and with Strombichides and Euctemon, to fight against Chios.
Title: Ancient Greek warfare
Content:  erstwhile Spartan allies, the Spartans were powerless to resist this invasion. The Thebans marched into Messenia, and freed it from Sparta; this was a fatal blow to Sparta, since Messenia had provided most of the helots which supported the Spartan warrior society. These events permanently reduced Spartan power and prestige, and replaced the Spartan hegemony with a Theban one. The Theban hegemony would be short-lived however. Opposition to it throughout the period 369–362 BC caused numerous clashes. In an attempt to bolster the Thebans' position, Epaminondas again marched on the Pelopennese in 362 BC. At the Battle of Mantinea, the largest battle 
Title: Second Messenian War
Content:  The Second Messenian War was the result of revolt by the helot population of Messenia, supported with the aid of the Argives and the Arcadians. In an attempt to regain freedom, the Messenians invaded Laconia. The first battle, the Battle of Deres, happened before the allies arrived. Aristomenes fought so well that he was made the new king of Messenia by his people. He followed this up by crossing into Sparta and placed a shield in the temple of Athena in order to scare the Spartans. This forced the Spartans to send to Delphi where they were told to gain a leader from Athens. Upon doing so the Spartans marched on the Messenians at Boar's Grave where they met Aristomenes and his troops, who defeated them. 

Question: who helped them recapture mycenae once they were old enough to fight?
Answer: Aegisthus.