I believe that the words that fit better to fulfil your sentences are not historical, but narrow enough to be presented thoroughly.
<em>To ensure that your research project is manageable, you must be sure that your topic is </em><em>narrow enough to be presented thoroughly.</em>
Even though selecting a good topic may not be easy, there are some things to have in mind, such as the topic must be narrow and focused enough to be interesting, yet broad enough to find adequate information. It is also important to make sure to know how the final project will look like before selecting your topic.
I can't say historical is the best word but it fits! It is important that something your research can actually be researched though it doesn't have to happen in the past. It has to be real, though.
South Sudan’s warring leaders agreed to cease hostilities and re-establish peace in their war-torn nation. This is not the first time they have made this promise.
