The "equality" between men on which democracy relies is an equality in the ability to harm.
When faced with the question of whether democracy is really the best political system, many retort with the old adage from Churchill: "democracy is the worst form of government, except for all those other forms that have been tried", and for them the question stops there. And yet, not only does the quote leave open the possibility that there are any number of better forms of government that have not yet been tried, but it is also subtly false, despite coming from a great man.
Indeed, while we see democracy steadily gaining ground in modern times, and seemingly coming to dominate the globe, it is not a purely modern idea. Ancient Athens had famously attempted it, as have some others, and it is likely that the basic concept fundamentally dates back to primitive humans living in tribes and selecting leaders. It is then curious that all these earlier instances of democracy have fizzled out, and proven less stable than many monarchies throughout the ages.
In defence from this observation, it is often claimed that the key difference between these more primitive democracies and the systems being implemented in modern times is the modern invention of the division of powers. However, while this is useful, it is hard to imagine why this should increase the dominance of democracies and not, say, monarchies. After all, one could plausibly replace the legislative branch with a king and his privy council, while keeping the other branches intact, and presumably the same beneficial effects of a division of powers should be conveyed to the monarchical system as well. On the flip side, it is also evident from modern examples of countries that drift somewhere between full democracy, totalitarianism, and one party rule in South America, Africa, and Asia, that an erosion of the division of powers is very possible even within an initially democratic system.
It then seems more likely that whatever the key advantage of democracy is, it emerged in modern times, making democracy the most stable modern political system. It is not necessarily the most beneficial for prosperity or growth, nor is it spreading because it is the absolute best system for its citizens; it merely enjoys a competitive advantage over the alternatives, given the present technology, demographics, and other factors. What then was the change that enabled democracy to overcome competing systems? I would postulate that it was the spread of easy-to-use, reliable, and cheap firearms.
Before the advent of firearms, even if a massive rebellion of urban citizens or of peasants emerged, it could be suppressed easily enough by force of arms. Sun Tzu wrote that a horseman was worth ten footmen, and one can imagine that a trained and well-equipped footman would be worth five peasants. On top of this equipment and training advantage of each soldier in the army, a professional army was trained to fight together, to hold ranks and use advantageous formations. The advantages of these were far larger in melee combat than they became once combat became a ranged endeavour. Before firearms became accessible to, and useable by, all, a small elite force could far more easily dominate the untrained masses in combat, thus controlling such an elite force was generally enough to retain power regardless of the opinions of the masses.
This changed with the emergence of firearms. Compared with older weapons, which required extreme amounts of training to use effectively, the training required to make use of rifles was fairly minimal (in this they were fairly similar to crossbows, but ultimately much more deadly). Now, while professional armies certainly still held advantages over lightly trained militias, these advantages were much smaller. Whereas in the past, controlling a small force was enough, even if most of the populace rose against you, now one needed to have at least some grip on the populace, as many rulers from Louis XVI to Muammar Gaddafi found out.
Democracy then, was simply a tiny expression of this new route to power. Instead of controlling the army, one needed to control the people, as, in the final reckoning, they became the strongest army. Whereas in, for example, a monarchy, someone could convince the populace that the monarchy is inferior and needs to be overthrown by force in favour of himself, in a democracy this person would simply be elected. This direct alignment of true power and the power allotted within the political system has made democracies more stable than the systems that were previously dominant. This does not, however, make democracy "less bad" than the other systems in any general sense, however, merely more appropriate for our time.
By now you may thinking that this is certainly an interesting theory, but even if true, all it does is confirm that right now democracy is the best. That may be true for a limited definition of "right now", but the times are changing, and they are changing quickly. Even now, drones are flying the skies, and by 2040 we will likely see manned aircraft phased out entirely in favour of unmanned fighters. Looking even further, it seems a near certainty that at some point this century (and I would say likely by 2070 or earlier), nearly all military forces will, in practice, be run by artificial intelligences at least on the tactical level. At that point, it won't matter how many civilians with rifles oppose such a force—a few people sitting behind the controls would be able to easily overpower them.
This will not be the end of democracy in any immediate way—social institutions have massive momentum, and, at least in some places, tend to persist for a long time after their prime—but it will probably mark the start of its global decline. Imagine that a strongman does come to power with the support of the military. There will be no popular revolution that can overthrow him. He will retain power as long as he can maintain the support of the military, regardless of what the average person on the street thinks—somewhat resembling North Korea, but without the need to indoctrinate the citizenry.
The new political systems that emerge after this change need not necessarily be all bad. After all, the dictators would not need to oppress the citizens, or suppress descent, since they would be able to simply ignore it. Some may even be benevolent. And, of course, the emergence of high quality AI is likely to be more disruptive than any slip in democracy in any case.
Regardless, democracy is unlikely to be here to stay. It is a system appropriate to a particular time, and to a particular balance of power. If you truly wish for there to be democracies forever, your best bet would probably be to attempt to globally outlaw all automated weapons (which is unlikely to succeed), or to allow, and perhaps even mandate, all citizens to own the highest-grade weaponry available (which may well have consequences more serious than the disappearance of democracy). I, myself, am not so attached to it. I would rather look forward to the best systems to come, rather than cling to one that happens to be best at the moment.
