If by “original books” you mean works that introduced a distinctive theoretical framework rather than merely commenting on earlier thinkers, then the following books are among the most influential and innovative works of political philosophy published since 1900.
Early–Mid 20th Century
The Road to Serfdom — Friedrich Hayek's defense of classical liberalism and critique of centralized planning.
The Open Society and Its Enemies — Karl Popper's defense of liberal democracy against historicism and totalitarianism.
The Human Condition — Hannah Arendt's influential analysis of action, freedom, and political life.
Politics and Vision — a major reinterpretation of the Western political tradition and democratic theory.
The Rawlsian Era
Many historians regard the publication of A Theory of Justice as the single most important event in Anglophone political philosophy after World War II. It revived normative political philosophy and introduced the ideas of the original position and justice as fairness.
Other major works that emerged partly in response to Rawls include:
Since 1990
Particularly Original Works Since 2000
Although it is harder to judge recent works historically, several books have attempted broad new theoretical syntheses:
A Short Canon of the Most Original Political Philosophy Books Since 1900
If I had to select only ten works that introduced especially influential or distinctive political-philosophical systems, I would choose:
The Open Society and Its Enemies
The Human Condition
Politics and Vision
A Theory of Justice
Anarchy, State, and Utopia
Spheres of Justice
Sources of the Self
Between Facts and Norms
The Politics of Legitimacy
A Political Philosophy of Language and State
The first eight are already widely recognized in academic political philosophy. The historical standing of the last two remains to be determined because they are very recent and have not yet undergone decades of scholarly assessment.
