Political Science

Introduction
It's the science of governance. It was created centuries ago.  Political scientists study governmental system and how policies impact society.  There are many different theories in political science.  Comparative Politics, international relations, political philosophy, public administration, and public law are important parts of political science.

History
Greek philosophers are the ancestors of political science.  Plato and Aristotle wrote books about politics. Machiavelli created political science.  He applied empiricism and realism to politics.  Voltaire, Rousseau, Diderot, and Thomas Hobbs had a big effect on political science.

Governmental Structures and Political Influence on Society
There are 3 branches of government in the US,  They are as followed: Legislative, Executive, and Judaical branch.  Ancient China had 3 main branches and 16 departments.  Different societies created different governmental structures at different times.

The policies government make have a good impact on some sectors of society and a bad impact on other sectors.  It seems like the Democrats are more socialist (State Capitalism: false socialism/true communism).  The Republicans are more capitalist.  Policies of Democrats will lead to US citizens being taken care of by the government.  This will cause great taxation, which will lead to less innovation. Republican policies will cause a greater income gap and quite possibly wipe out the middle class. Republicans favor the rich and care less about the poor.

Theories of Political Science
Behaviorism: Its the study of how politicians act, speak, look, and stand.

Contractualism: People made agreements to establish a government.

Communism: The idea is everyone will be happy will class is dissolved.

Constitutional: A set of laws written down that rules for government and commoners.

Modernization: The belief was countries become more modern as they become more European. Modern means behaving like European.

Neo-Institutionalism: People that followed this theory; look at how institutions affect society.

Rational Choice: People try to make the best decisions for every situation.

Systems Theory: It looks at how various variables interact with each other.

Breakdown of PS
Comparative Politics: It's comparing and contrasting policies of different countries.

International Relations: The study of how countries communicate and negotiate with each other.

Political Philosophy: Is the philosophical study of political ideas.

Public Administration: The study of how government implement policy.

Public Law: Government laws that relate to citizens.

Conclusion
If you want to know how countries are govern, you should study political science.  This is a great science!  I like the complexity.  Check it out.    

References
http://desart.us/courses/1010/pstheories3.html 
http://www.philosophybasics.com/branch_political.html
https://en.wikipedia.org/wiki/Political_science
https://en.wikipedia.org/wiki/History_of_political_science
https://en.wikipedia.org/wiki/Niccol%C3%B2_Machiavelli