Plato thought that it was democracy which lead to tyranny in the classical Greek sense; when the mob grew strong enough to oppose all previous concentrations of power, an ambitious leader would take up the cause of the mob and use them to crush the existing institutions and establish their own unrestricted rule. While the connection with democracy is not so straightforward as Plato suggests, there is an important element of truth in this. A tyrant in the classical Greek sense certainly did tap into new sources of power and use them to crush existing institutions, rather than simply making deals with existing institutions and thus facing the constant danger that the established powers would decide to back out of the alliances.
One of the reasons for the remarkable performance of the French army during Napoleon's wars was Napoleon's method of replacing losses in the officer corps. Enlisted soldiers who displayed conspicuous bravery would be promoted to officer rank. It was possible for any old commoner who joined the army to rise to any rank by such promotions. Most of Napoleon's enemies had policies of recruiting only aristocrats as military officers, with rank in the army heavily influenced by aristocratic rank.
There were disadvantages to Napoleon's system; aristocrats tended to be better educated, and those who served in the military generally would have had some training in military science. However, Napoleon's system had much more important advantages.
First, it contributed greatly to the morale of the French soldiers. Since their officers were generally conspicuously brave (or else they wouldn't have been promoted to become officers), the officers set a strong example for the troops. They also understood the troops better, having come from among them. The possibility of becoming an officer encouraged both loyalty generally, since it increased the potential rewards of military service, and courageous effort, since that was the way to gain those potential rewards.
Second, it meant that Napoleon had no trouble replacing losses in the officer corps (or at least no more difficulty than he had in replacing the common soldiers). Such losses were by no means infrequent, and Napoleon's enemies seem to have been put at a great disadvantage in replacing losses by the fact that they recruited officers only from the aristocracy, and the most martially inclined aristocrats were already in the army, so they had to recruit less promising candidates and in some cases simply get by with fewer officers when they raised new forces after heavy losses against Napoleon.
Still, quite possibly the most important value of the policy for Napoleon is that it meant his officers tended not to be connected to existing institutions of power, and so were less likely to be troubled by divided loyalties. This also had the disadvantage of making existing institutions of power more hostile to him, since he was further excluding them from power, but the French revolution had already greatly weakened such institutions, and Napoleon preferred to continue that process in order to further concentrate power in his own hands. Probably the most successful tyrant in history, Augustus, preferred to employ freed slaves in many top-level administrative positions despite his own patrician background, with similar benefits.
What relevance does this have for the modern world? Well, relying on alliances with institutions of power makes a tyrant weaker. So tyrants who depend on foreign support, to take one example, are predictably weaker than those who do not. Thus, even if a dictator can sometimes produce greater political stability, it's generally a bad idea for outsiders to support a dictator with such a goal in mind; by doing so, they reduce the chances that the one they support will turn out to be one of the successful ones, and so that they really will provide stability. Sadly, U.S. foreign policy does not ever seem to have noticed this, despite providing plenty of empirical evidence for the thesis in the record of its failures. Given the length this blog post has already reached, I will leave other lessons as an exercise for the reader.