Alexander was one of the most successful military commanders of all time and it is presumed that he was undefeated in battle. By the time of his death, he had conquered the Achaemenid Persian Empire, adding it to Macedon's European territories; according to some modern writers, this was much of the world then known to the ancient Greeks (the 'Ecumene'). His father, Philip, had unified most of the city-states of mainland Greece under Macedonian hegemony in the League of Corinth. As well as inheriting hegemony over the Greeks, Alexander also inherited the Greeks' long-running feud with the Achaemenid Empire of Persia. After reconfirming Macedonian rule by quashing a rebellion of southern Greek city-states, Alexander launched a short but successful campaign against Macedon's northern neighbours. He was then able to turn his attention towards the east and the Persians. In a series of campaigns lasting 10 years, Alexander's armies repeatedly defeated the Persians in battle, in the process conquering the entirety of the Empire. He then, following his desire to reach the 'ends of the world and the Great Outer Sea', invaded India, but was eventually forced to turn back by the near-mutiny of his troops.