This is an important question. The main topic of a paper is the most important element of a paper. It is called a thesis statement. To put it as simply as possible, the thesis statement is what your paper is about. A good thesis statement is debatable and has evidence to back up its claims. For example, if you are writing a paper on the Romans and your thesis is: Roman warfare is superior to Greek warfare, then a successful paper should give several reasons why you think Roman warfare is better. These are your supporting points. At this juncture, you can say something like: Roman warfare is superior to Greek warfare, because the Romans had better equipment, better generals, and a better understanding of military technique. For a really good paper, you might want to counter potential arguments to show that you thought about your thesis on many levels. One final advice. Take time in crafting a good thesis statement. This is by far the most important part of your paper.