To think about whether structural developments or great individuals have a bigger impact on the way that history plays out, consider Abraham Lincoln and the end of slavery in the United States. It’s possible to argue that without Lincoln’s leadership and conviction, slavery would have continued. As such, he made history not only in the North’s defeat of the South but in emancipating the slaves.
However, other historians minimize Lincoln’s role and focus on general structural developments. Howard Zinn, for example, suggests that the structure was already in place for slaves to liberate themselves. According to Zinn, there’s plenty of evidence to reasonably argue that slaves were becoming increasingly militant and resistant to the brutal forces of slavery. In this scenario, Lincoln didn’t free the slaves. He saw that the apparatus of slavery was unsustainable and thus interceded so that the federal government could control what happened after slavery’s inevitable downfall.
Indeed, after the slaves were declared free, the structure and condition throughout the United States remained vehemently racist—a fact that makes some people question the greatness that's often attributed to Lincoln.
Using Lincoln as an example, one might see why it’s not so easy to separate structural developments from the individuals that comprise them. At any historical moment, it’s feasible to simultaneously argue that the structure and the individual had the greater impact.
Even when it comes to the nefarious history of Nazi Germany, it can be hard to attribute what happened to one individual. While countless books and documents present Adolf Hitler as singular, once-in-a-lifetime figure, Hitler did not create the structure of genocide, nor was he the first (or last) head of state to use lethal persecution and constant war to further his political agenda.