Choosing a topic for your extended essay is on of the most critical aspects of the entire task. The most important part of choosing a topic is breadth vs. depth. With the extended essay, you want more depth. It is critical that you have a focused research question. Your advisor can help you narrow down your subject into an appropriate question.

For example, a paper about the Great Depression is too broad. A paper analyzing the impact of the government's response to the Great Depression on current Federal Reserve action would be an appropriately focused question.

Another important aspect in choosing a topic is to choose something in which you have a genuine interest. This will definitely make writing the paper tolerable, or maybe even enjoyable...

You should review over several subject guides to ensure you are comfortable with the subject you choose.

Remember - this is a research paper, not a book report or review of a subject. You need to have a question established to which you are seeking an answer.