What is it?
Geography defines territoriality as efforts to control pieces of earth's surface for political and social ends.
An example of this could be religious conflicts such as Ireland and England. A large portion of Norern Ireland is a Catholic Nation and many of the citizens do not want to be part of anon-Catholic/Protestant nation such as England.
How do I memorize this?
An easy way to remember territoriality is by thinking of personal space. Personal space is our own "territory" in which others do not invade unless granted permission.