How to create a hypothesis for a historical research? When writing a dissertation or a thesis about history, students and researchers are asked to state a problem and a hypothesis for that problem. My question is how to state a problem and a hypothesis for a historical event where we all know that history never changes and that it is restricted to already given facts?
Supposing that someone is writing a thesis about the Battle of Waterloo ...All the info about the Battle of Waterloo are the same everywhere, what can this researcher add?? Nothing actually, he/she is going to end up summarizing a dozen of books about it without bringing anything new to the topic (not because he/she cannot but because it's history).
What kind of problem statement that one can write about a Battle, a king, a conflict, ... 
I mean how can someone see problems in history and give hypotheses for them??
Please illustrate if you can
This sounds like trying to force a restricted view of the scientific method to research in history. One learns during many years of studying history how research in history is performed, what is expected, what constitutes verification and evidence, just as one learns during many years of studying mathematics how research in mathematics is performed, what constitutes proof, the accepted standards of rigor, etc. And similar things can be said about Physics, Computer Engineering, Linguistics, Philosophy, Comparative Literature, Botany, Aerospace Engineering, Archaeology, etc.

Here's one way to at least superficially research your question without going through years of study in history. First, search for "Battle of Waterloo" (without quotes) in the title field at the ProQuest search page. Then google the titles of some of the (over 40) results to see whether freely available copies can be found. Then, for the theses you are able to get copies of, look over the abstract and/or introduction and/or summary, using the table of contents to locate these if you can't immediately find them.

When I did this, the 7th listed item was Waterloo in Myth and Memory: The Battles of Waterloo 1815-1915 (2013), and its abstract begins with the following:


  This work examines memory of the Battle of Waterloo. There have been hundreds of works on the Battle of Waterloo but what this work does is to examine how works in several genres change over time. The memory of Waterloo was not static but changed several times over and over again. The myth of Waterloo was created, challenged and renegotiated several times.