The author sought to overthrow centuries of fallacious thinking on the subject of the state's origin, nature, and purpose, put its it place a view of the state that constitutes a foundational attack on the structure of modern society.
He utterly demolishes the social-contract view of the state as it had been advanced by most thinkers since the Enlightenment. He seeks to replace that view with a realistic assessment of the state, one that can only make anyone with statist leanings squirm: he sees the state as composed of a victorious group of bandits who rule over the defeated group with the purpose of domination and exploitation. It achieves its status through a form of conquest, secures its power through relentless aggression, and sees its main function is to secure its status and power.
From an economic point view, his analysis holds up even where his language about capitalism and socialism can be somewhat confused. In fact, it was Rothbard's own work that took Oppenheimer's theory and fit it into a free-market framework. But to fully understand the state theory behind modern Austro-libertarian thinking, this work is indispensable.