Are modern handguns a major reason for democratization?

The availability of weapons to ordinary people has often gone hand in hand with with democratization. Early Greece and Rome were blessed by hilly terrain that allowed yeoman farmers to produce high value added crops like grapes and olives, that could be traded for cheaper wheat and cloth, leaving a surplus for them to buy their own weapons. Plus the fact that their hills were easy to defend against "slave" conscripts of nearby empires. (The following example is my own.)

http://bleacherreport.com/articles/360155-march-10-2010-marathons-2500th-anniversity-celebration

The invention of the stirrup helped create the feudal system. Once riders could be stabilized in horses, not even Roman-style infantry armies, never mind peasant levies, could stand up to cavalry, meaning that rich knights on horses terrorized poor peasants, forcing them into serfdom.

The feudal system STARTED to break down when better anti-cavalry weapons (halberds and pikes) were developed, and placed in the hands of mountaineers like the Swiss (who also benefited from terrain that was not good for cavalry).

But it was the invention of the cross bow, long bow, and later gunpowder, that led to creation of missile weapons that could penetrate armor, putting ordinary peasants on close to an equal footing with knights. The later development of long-range and "repeating" rifles (and pistols) equalized things further.

It may be no accident that in the U.S., Wyoming was the first state to give women the right to vote. It was also a frontier state with the most guns (pistols) per capita, that put women on the most equal footing with men.

If we compare the power of weapons that could be used by the state and those that could be used by the guerrillas and militants, we should conclude that the further we go into the past the closer were the means employed by the rebels and the state.

In ancient times people used cold weapons such as sword, lance and shield. Of course the state army usually had superior weapons, but one could use some non-weapon things such as knives or pitchforks or just clubs to counter-act the army.

Once the body armor was developed, it became much more difficult for irregular units to fight the pro-government forces.

The firearms already require special factories, and actually cannot be balanced by the cold weapons. In most countries possession of firearms is prohibited, and even if the rebels have some, they need bullets for them which also require technology to be manufactured. So the army can easily crush any rebellion unless the rebellion is continiously supported by a foreign power or a part of the army.

But the small arms still can be used by the rebels even if they cannot produce them. This is not the case with tanks and planes which require extensive infrastructure and trained personnel to use. With the invention of this kind of weapons the state got unprecedented superiority over any rebels unless they are openly and extensively supported by a technologically advanced power.

With the invention of the nuclear weapons the gap even further increased so now nuclear-possessing countries have ultimate military superiority not only over any rebel forces but also over any non-nuclear state.

That said, any modern army can easily crush any open rebel resistance if it is loyal to the government, the government is not threated by an even more advanced foreign force and the morality questions not considered. This was not the case of Ancient Rome for example, where the government not always was able to defeat a rebellion.

The only possible tactics for rebels now are to disguise themselves as civilians, to incite the military to take their side or to seek a foreign aid.

I'm not sure. The democratization in the XIXth century was also due to the increasing power of labour movements, which was not gained by the use of weapons, but by strikes, mostly. When industrialists rule the political system, the labour class doesn't need to shoot - all they need to do to exert influence is collectively refuse to work.

The rise of democracy and the fall of feudalism are two separate questions, though arguably the latter was a prerequisite for the former.

It is possible that cheap hand guns were a minor factor in either of these, but I doubt it was a major factor. The importance of cavalry in the Middle Ages shouldn't be exaggerated: infantry and archers were usually more plentiful and cheaper to support. Except on a plain, cavalry normally didn't have the advantage, and a good commander wouldn't let his army fight on a plain if the enemy's cavalry was superior. There were always hills and forests and swamps and whatnot, in which cavalry was fair game for archers and couldn't gain the speed required to trample infantry. Of course cavalry could be powerful, but the army with the most knights didn't always win.

The rise and fall of democracy in ancient Athens obviously has nothing at all to do with guns, nor has the rise and fall of the Roman republic.

The "fall" of the feudal system took about a millennium, and there are still vestiges of it in our modern culture. A very important underlying reason why the power of the nobility decreased from the central Middle Ages onwards was the increase in trade and the increasing power and wealth of the cities as compared to the country. The mayors of a wealthy trading port often came to be as powerful as high nobility. Of course circumstances varied across Europe, but I think this is the general picture. I think Rincewind has mentioned some important factors that facilitated or led to democracy.