Well, politics is studied through the humanities (e.g. history and philosophy) and the social sciences (e.g. sociology and economics). Therefore politics is largely informed by these disciplines, or at the very least political actors usually try to establish legitimacy through these disciplines. There are also interdisciplinary fields of scholarship specifically devoted to what we generally refer to as politics; most notably political science and public administration. So it would stand to reason to look up some introductory books from these disciplines.
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My introductory recommendations for you, not all necessarily leftist:
Well, politics is studied through the humanities (e.g. history and philosophy) and the social sciences (e.g. sociology and economics). Therefore politics is largely informed by these disciplines, or at the very least political actors usually try to establish legitimacy through these disciplines. There are also interdisciplinary fields of scholarship specifically devoted to what we generally refer to as politics; most notably political science and public administration. So it would stand to reason to look up some introductory books from these disciplines.
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My introductory recommendations for you, not all necessarily leftist:
For history A people's history of the United States by Zinn, Ways of the world by Strayer & Nelson
For philosophy What does it all mean? by Nagel, Think by Blackburn and What philosophy is by O'Hear; on the overlap of history and philosophy Radical Enlightenment by Israel (considering how important the enlightenment is for contemporary thought)
For sociology Sociological Theory by Ritzer & Stepnisky; politics from a sociological perspective Globalization and the state edited by Schinkel
For economics Economics by Stiglitz & Walsh; on the history of capitalism Talking to my daughter by Varoufakis
For political science Comparative government and politics by Hague, Harrop & McCormick
For public administration Implementing public policy by Hupe & Hill
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^(If you have trouble finding the books, try getting access to aaaaarg. More information on that in) ^(this subreddit's sidebar)^(.)