The Art of War

As others have noted some of the tactical advice is thousands of years out of date, but the vision of strategic issues is still very relevant. This edition is well written and an easy read.

It does not take an interest in the military to make this a great read.
It is also a great read for anyone interested in politics and will help one to understand the antics of folks like James Carville.

Sun Tzu is also the foundation of much of the work of Col John Boyd that has had such a major impact on the current military.

A reader of Sun Tzu might have a very different take on why there has not been a massive terrorist attack on America after 9-11. One of his basic principles is to separate the population from the enemy leadership. Clearly 9-11 connected the leaders with the population. The absence of an attack has allowed the anti-war movement space to become effective.

Knowledge of Sun Tzu is most helpful in understanding a major force on current world leaders from Chinese leadership Muslim fundamentalists.