The very first line says a castle is a defensive structure,  the article goes on to say that a castle is also used for offensive or political purposes.   I say it should be a fortified structure, One could delete the word defensive from the first line, so as just to say a castle is a structure.   The first paragraph says that castles are found in Europe and the Middle East (Middle East should be replaced with a more specific location) and then the article goes on to say that there were castles in the Americas.  'Fortaleza Ozama in the Dominican Republic was the first castle built in the Americas.' - 