When you're writing a research paper and your teacher has assigned you a subject, you need to be aware of four basic elements, before you choose what to write on.

• Subject: a very broad category, a general area of interest, usually assigned by your teacher. When the teacher assigns a subject, this does not mean that you have to cover the whole area of knowledge within this subject. Mind that subject is not topic, and if you want to write a good paper, you need to narrow it down to a specific, researchable field.
• Topic: more specific focus within the general subject, developed by the student - the narrower, the better. But this is not the end of your work in defining what to write on, as you have to come up with research question.
• Question: the best topics are built around intriguing questions.

Now, once you've got a topic, you next need to define a question that you've got to answer while writing your paper. The best topics are usually built around intriguing questions that the student actually is interested in answering.

So, if you history subject is, say, Abraham Lincoln, and you narrowed it down to topic of the election of Abraham Lincoln in 1860, here's one possible question that you might want to ask yourself about Lincoln's election in 1860: how did Lincoln an obscure politician from the Midwest, win the crucial 1860 election against better known competitors? Once again, this works well for a paper of 10-15 pages, anyway, it's a kind of question that could probably be answered reasonably well in a paper of that length. If you were going to write about much broader topic, the questions would be equally broad, and again, almost impossible to answer in just 10-15 pages. For example, there have been many full-length biographies of Lincoln, built around a question: what made Lincoln a great President? And there's so much to say about that - about his personality, his political skills, his reaction to the great issue of his days, and so on and so forth there's so much to say there, and you will almost need to write 300 pages to answer that question effectively. With much narrower question, focused only on him Lincoln managed to win the 1860 election, there's something that could be covered reasonably well in just 10-15 pages. It's an interesting question as well, and therefore it will work well for readers to define what your paper is going to be about.