Short Version -- This is a summary of the important issues covered in this section of the U.S. Constitution. 

• The U.S. guarantees every state a representative form of government.
• The U.S. will protect states from invasion and civil unrest.

Long Version -- This is the text of the Actual U.S. Constitution. 

The United States shall guarantee to every state in this union a republican form of government, and shall protect each of them against invasion; and on application of the legislature, or of the executive (when the legislature cannot be convened) against domestic violence.