But when the right person with the right resources at the right time is there, magic happens. All three legs of the stool have to be there.
You need a leader to inspire your troops. Otherwise they start thinking "what am I doing here I just want to survive and go home".
We seem wired to rally around leaders to get things done. Most people seem to wait around to be told what to do. This makes modern people very uncomfortable (for some very rational reasons) to the point that we engage in denialism about it.
In ancient tribal societies with group sizes close to Dunbar's number, this probably worked out much better than it does now. People had direct relationships with the leader and could see clearly what was happening, and if a leader lost favor they had to face people directly. Sometimes the results were brutal.
In modern society we have systems so large with so many layers of social and economic abstraction that it's very easy for leaders to abuse their power and to hide that abuse for a long time. It's also very easy for leaders to lose sight of the "ground truth" and/or for the people to lose sight of what the leader is doing. I'm sure sometimes leaders don't set out to abuse their power but kind of "back into it" for various reasons. It gets pretty dysfunctional but when you think about it it's kind of astounding that we are able to scale at all to societies this large given our species' background.
Edit:
I also wonder if there's an ego protecting mechanism at work. When Elon Musk says he's going to build a reusable rocket, we can get behind him and work for him... but if the effort fails we can blame the whole thing on him. If we succeed the leader gets the credit, which is the part we hate, but if we fail the leader also gets the blame.
Still... I am not familiar with many examples of cases where the leader was removed and not replaced and things didn't fall apart.
I would like to see more experimentation in this area though. We don't experiment nearly enough with social structures.
Mmm as far as experimentation, the closest I can think of on a large scale (besides anarchist groups which never had leaders) is that in Europe when a government can't be formed, they can operate without any official leadership even though there's a caretaker government (usually the previous one, who don't have a mandate anymore) but that's kind of formal. Big cooperatives usually elect leaders, so they still have them even though they're elected and can be recalled.
A pervasive theme is that time rumbles by and great men merely cling on and go with it at the right time. The Greeks were in the mood for a rampage and off they went. An Alexander born today won't start conquering foreign lands.
And yet, I can't shake the feeling that there must me something unique to Alexander and others.
Time passes, but not everybody massages it just enough to make a change.
The great man way of describing history leaves a lot to be desired but the "somebody else would have done it" crap is even worse. Remove key figures from history and then try to judge what would have happened had someone else filled their shoes and it becomes painfully obvious. Imagine 9/11 happened +/-20yr. How would the second half of the 1900s played out had Chaing Kai-shek gotten control of mainland china? Would we have gotten the napoleonic wars if Louis XVI kept the throne another 10yr? What would european history look like if church had waited another 200yr before cooking up the idea of the crusades? Imagine if the US hadn't elected an abolitionist sympathizer in 1860 but instead waited until 1872? How would recent European history look without Stalin? Etc. etc. Key details regarding when and the order in which events happen have a huge impact on history and the whims of individuals (like Alexander) massively influence these details.
I'm not here to defend the great man theory of history. I'm here to put the "it mostly would have happened about the same" theory of history in the dumpster where it belongs.
Except for that it is not so much the exception as it is the rule.[1]
People followed in their leadership and did their bit, every piece of the puzzle fell into place.
How do you know that? Leadership and management are real jobs but there's often existing demand, goals and plans that these people are employed by those around them for. I'm willing to go out on a limb and wager that's the way it always is actually. Everyone's a product of their environment and their times, standing on the shoulder of giants, workers and peasants alike.