Some scholars of history disdain counter-factual scenarios or, as they are popularly known, “what if” questions about the past, as a fanciful waste of time. They are wrong. As some of our most distinguished contemporary historians like Niall Ferguson and Andrew Roberts often point out, they are extremely helpful in understanding the past as well as our current dilemmas.

While some people who write about history are determinists and act as if everything that wound up happening was predestined to occur, the truth is that no one ever knows what the future will bring. Whether because of a matter of chance or factors not fully appreciated at the time, any single action can change what follows. As Eugene Rice, the eminent scholar who once chaired Columbia University’s history department, taught me a long time ago, everything in history is “evitable.” Unless you examine those “what if” scenarios, which might have led to very different historical outcomes—whether losing wars that were won or the absence of leaders who made a profound difference—you can’t fully appreciate how history turned out.

Or, for that matter, the world we must live in today.