With their defeat of the Spartans, Thebes, at the head of the Boeotian League, became the dominantforce of Greek politics, supported by the Arcadian League which they had set up in the south to balance out Sparta. The growing Theban power drove together the former adversaries Sparta and Athens, as well as a number of lessor powers with grudges against Thebes or their allies such as the Mantinea League and the Eleians - still smarting from the Arcadian capture of Olympia. When Athens sent a force of hoplites by sea to Lakedemonia to assist the Spartans in 362 BCE, Epameinondas, who had been the principle architect of the Spartan defeat 9 years earlier, marched south again. The two armies met at Mantinea, and the Theban alliance was victorious in the battle, but Epameinondas was killed fighting at the front of his men (pictured here), as were both of his lieutenant commanders, and Thebes felt compelled to offer peace terms to the defeated, capping the rise of Theban power and preventing their hegemony over the Greeks. The three centers of power - Athens, Thebes and Sparta - all remaining relatively weak and antagonistic to each other, were thus ripe for the conquering by Phillip II of Macedon, and his son Alexander, over the next two decades.