The Seven Military Classics Of Ancient China : Sun Tzu isn't the only military strategist on the block.
Kaplan and Sadock's Synopsis of Psychiatry: I make sure to study at least one university/high school textbook on any subject that I find interesting.
Also, not reading but watching Professor Jiang Xueqin's lectures [0] has been pivotal towards helping me find new avenues to research and understand geopolitics .
Here is a partial list in no specific order (lookup their reviews on Amazon/elsewhere on the web for details);
1) The Pocket Oracle and Art of Prudence by Baltasar Gracian translated by Jeremy Robbins. This book is also available as "The Art of Worldly Wisdom" translated by many others. Of these the one by Christopher Maurer is noteworthy.
2) A Pocket Mirror for Heroes by Baltasar Gracian translated by Christopher Maurer.
3) The Prince by Niccolo Machiavelli. Of the many translations, the one by Peter Bondanella in Oxford World's Classics is noteworthy.
4) Maxims and Reflections (Ricordi) by Francesco Guicciardini translated by Mario Domandi.
5) The First Great Political Realist: Kautilya and His Arthashastra by Roger Boesche - A very nice summary of the magnum opus "Arthashastra" from Ancient India.
6) King, Governance, and Law in Ancient India: Kautilya's Arthasastra translated and annotated by Patrick Olivelle - A very good and modern translation of a large text.
7) The Essence of Politics (Sanskrit: Nitisara) by Kamandaki translated by Jesse Ross Knutson - A shorter Ancient Indian text in the vein of Arthashastra.
8) The Pancatantra: The Book of India's Folk Wisdom translated by Patrick Olivelle.
9) Tirukkuṟaḷ by Tiruvalluvar (see https://en.wikipedia.org/wiki/Kural for details) - For a good English translation see the one translated by P.S.Sundaram and published in Penguin Classics.
10) The Art of War by Sun Tzu translated by Ralph D. Sawyer.
11) The Seven Military Classics of Ancient China translated by Ralph D. Sawyer.
12) [The Complete] Book of Five Rings by Miyamoto Musashi translated by Kenji Tokitsu.
I have left out the obvious works by Epictetus/Seneca/Cicero/Marcus Aurelius/etc. since they are all well known.
The above is a good representative of the three categories drawn from different cultures and should get you started.
