The History of The Peloponnesian war is exactly what it sounds like. One of the first written historical accounts, it delves into the Peloponnesian war in ancient Greece.
Written by Thucydides, an ancient philosopher and general of Athens during the war, he gives a firsthand account of the war and what it meant to those fighting. He mixes military and historical accounts with his own thoughts on the war and its reflections of the world at large.
One of the best modern translations is the Cambridge edition 1 translated by Jeremy Mynott and released in 2013. If you're a first-time reader, you should start with this edition. The 2 Landmark edition of Thucydides is also quite popular as it provides additional maps that give the reader a lot of context. However, one downside is that it is based on a translation from 1874, and the Victorian English can be dense and off-putting for a first-time reader. 3 Martin Hammond's translation by Oxford World Classics is clear and easy to read; the forward can be a little tedious so if it's your first read you can just skip it. If you want to delve in to Thucydides but don't want to know every battle in-depth, Paul Woodruff has a great book of excerpts of Thucydides 4 published by Hackett.