I am of course familiar with the basics of Alexander’s life and campaigns, but I’ve never quite understood how the King of a tiny Macedonian kingdom managed to subdue all of Greece (minus Epirus), let alone conquer Egypt and Persia. Where did he get all these soldiers from? And if he had the power to conquer all the way to India, why didn’t he take Epirus?
Interesting question! I cannot answer this myself but there are some earlier threads I can link to which may be of use.
Our u/Iphikrates has written a fair bit about this question in various places. In this answer he explains how Macedon became the dominant power in Greece (which seems to have happened mostly under Alexander's father Philip), and here he has an interesting discussion on how the Macedonian army was assembled, what the differences were to Persian and Greek armies, and further down how much of Alexander's army was in Macedonian and how much was allied Greek. He has also written in this response about the unimportance of technological differences for Alexander's victories.
Hopefully this may partly answer the question, but new responses are very appreciated!