The more I read of history, the more convinced I am that history turns, in the words of Jeff Greenfield, "not on a dime but on a plugged nickel." In other words, history often turns on what contemporaries may view as miniscule decisions -- for example, a split-second impulse to exit stage-right instead of stage-left, where a leader is met by an assassin, or not. A chance meeting in which one hears about a job opportunity, a decision to apply for a job, an employer's decision to hire a worker.
Students of history could come up with literally hundreds of case studies of miniscule decisions, as well as accidents and chance -- that changed a nation's history or even world history. Or identify movements or waves or clashes of values and economies so powerful that no matter how many times individuals faltered, took wrong turns, or sought to avoid conflict, those movements or waves or conflicts would eventually alter the course of history.
Margaret Thatcher's biography, "The Downing Street Years," offers just one of thousands of history's slender threads. Parliament's vote of "no confidence" in her predecessor prime minister, John Callahan, occurred because just one Irish MP showed up late and abstained. If he had voted otherwise, there would have been no general election at that time and quite possibly no Thatcher government.