Countries today face a myriad of issues that threaten to divide its citizens. Religious differences, for example, can split people of the same culture. Differences in language can be a cause for unrest, and may require resolution by the central government.
The Heartland Theory is a form of geopolitics. Geopolitics are politics influenced by geography. Since human geography is about how humans are impacted by geography, we would say geopolitics have a lot to do with APHG. The Heartland Theory is important to anyone taking the AP® Human Geography exam.
Often times you think of learning vocabulary as a memorization drill. This is a huge a misconception. Learning vocabulary has more to do with understanding the meaning of a word and improving your word power than simply remembering the meaning for a short period of time. The words you learn should stay in your memory forever, and not just until the exams are over.