In 1962, the eminent statesman Dean Acheson enunciated a principle that has dominated global politics ever since: that no legal issue arises when the United States responds to a challenge to its 'power, position, and prestige'. In short, whatever the world may think, US actions are legitimate because they say so. Spanning the impact of Edward Snowden's whistleblowing and Palestinian-Israeli relations to deeper reflections on political philosophy and the importance of a commons to democracy, Because We Say So takes American imperialism head on.