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.
Yes julius Caesar was a genius in military strategy
Collective bargaining was used by unions to allow the union leaders to negotiate wages, labor contusions, etc with employers. The goal was to increase wages, better working conditions, etc.
