Montesquieu’s ’The Spirit of the Laws’ [PDF ebook] 
A Critical Edition

The Spirit of the Laws not only systematizes the foundational ideas of "separation of powers" and "balances and checks, " it provides the decisive response to the question of whether power in the nation-state can be limited in the aftermath of the Westphalian settlement of 1648. It describes a civilizational change through which power becomes domesticated, with built-in resistance to attempts to absolutize (or make total) political power. As such, it is the Bible of modern politics, now made more accessible to English readers than it ever has been.