I mean, he conquered a lot of territory. Like, a lot. His father Philip had conquered all of Greece, but Alexander did what the Spartans and the Athenians had failed to do. He destroyed the Persian Empire. He conquered all the land the Persians had held, including Egypt, and then marched toward India, stopping at the Indus River only because his army was like, hey, Alexander, you know what would be awesome? Not marching. Also, Alexander was a really good general, although historians disagree over whether his tactics were truly brilliant or if his army just happened to have better technology, specifically these extra-long spears called sarissas.