In an explanatory essay, or any essay, the introductory paragraph introduces (hence it's name) the main idea, or what you are going to explain. The body paragraphs go into extreme detail of what the introductory paragraphs mentioned.
North and West. USA and Russia. Let me know if that's correct.
Answer:
Their Ideologies, beliefs, and access to reliable information.
C. the assassination of the Archduke.