I wrote a couple of undergraduate papers on Greek military history. You could look up Hans van Wees book on Greek warfare, it is a perfect starting point.

H. Wees, van, *'Greek warfare:myths and realities, *Bristol classic press 2004

Example of question: 'What part of Greek warfare in the Classical period was directly or indirectly altered the most due to the collision between the Greek Poleis and the Persian Empire? **