There are topics and questions in life that have correct answers. If you multiply seven by eight, for example, you should get fifty-six every time; if someone asks you what you get when you combine two hydrogen atoms with a single oxygen atom, the answer will always be one molecule of water. And if you're not so sure, a simple calculation to verify either of these questions will bear out that there is one and only one correct answer. These topics offer certainty.
Not so with history. Our knowledge of history is only as good as the evidence left behind and the surviving opinions of those eyewitnesses who wrote about their experiences (and then, of course, the opinions of those who wrote about the opinions of those same eyewitnesses). "What" happened is usually (though not always) a simple question to answer: "Germany invaded Poland on September 1, 1939," or "Neil Armstrong set foot on the moon on July 20, 1969," but "why" is a much tricker -- and more satisfying -- question to attempt to answer. History is uncertain, and though it lies firmly in the past* (which is pretty much its sole defining characteristic), our understanding of “why” is ever-evolving. Given the evidence to back them up, two intelligent people can reasonably argue diametrically opposed opinions on "why." Such arguments often become more heated and emotional than you would expect; our own views, whether honed through school classes, self-directed study, or personal experience, are very dear to us and we humans do not easily change our perception, even that of events that began and ended long before we were born.
These arguments will almost certainly never be fully settled one way or the other. Much as it would be incredible (for me as much as for you) if there were authoritative evidence of how and why each historical event occurred, that’s not the way it works. History clings to its secrets. We may never know, for example, precisely who Jack the Ripper really was. There are fascinating theories aplenty, and bits of evidence to back up each of those theories. However, there has been no smoking gun, no diary containing the words, “Yes, I, Mr. Montague John Druitt, am indeed the killer of prostitutes known to London as Jack the Ripper,” no DNA evidence from under the fingernails of any of his victims, no teary confessions, nothing that anyone but the most determined and biased advocates would ever consider to be definitive evidence. This story will almost certainly forever remain one shrouded in mystery by time and by what would now be considered to be the rudimentary policing/forensic procedures of the 1880s.
There have been over 100 men put forward over the years as Jack the Ripper suspects, including such well-known figures as Lewis Carroll (yes, the author of Alice in Wonderland) and H.H. Holmes, one of America’s first serial killers. And to this day, devotees of the story will argue their pet theory with all of the passion they can harness. Yes, nearly 130 years later, we still wonder and debate the identity of a single man who, historically speaking, didn’t even kill that many people! Books proclaiming that they have identified Jack the Ripper once and for all still make their way off the presses with regularity. One of the most recent of these is Naming Jack the Ripper, by Russell Edwards, published in September 2014. The author claims, using DNA evidence from a shawl purportedly belonging to one of the victims, Catherine Eddowes, that Jack the Ripper was a Polish Jew named Aaron Kosminski. Other Jack the Ripper enthusiasts immediately proceeded to rip his DNA evidence and methodology to shreds.
That’s the way of history; the argument is more available than the fact, and is almost always more fun.
*This is not to say that I do not believe that history affects us every day. If I didn't believe that, I would probably be doing something completely different with my life.