I've actually written about this previously when prompted about the 'modern guerrilla'. Hopefully this might be of some help:

The real origin of modern guerrilla warfare can be found in Mao Zedong and the Chinese Civil War. Beyond creating an actual theory for which you could base how to fight a guerrilla war on, Mao Zedong's victory in the Chinese Civil War and those that came afterwards signified the fact that guerrilla warfare had now become politicized. No longer was it only about fighting - you had to gain people's support for your cause. It meant that guerrilla fighters also had to be politically aware and that their leaders adapt to the 20th century. Thus, propaganda became vital and the concept of engaging an international audience in your cause was developed through the use of printed material to the radio and finally to television and the Internet in the modern age.

The Maoist theory of guerrilla warfare is deceptively easy: First, you gain the support of the people. You make the people politically aware, get them on your side so that you can gain a refuge, food and manpower for what was to come ahead. You create a base in which to function from. You also create a broad, united front in which you engage the entire people, no matter their political background, for one cause. Second, you begin the guerrilla war. Hit-and-run, ambushes and everything that would associate with asymmetrical warfare would occur on this stage. The third stage is the final stage and the most important one. It is here that you are prepared to go from a unconventional guerrilla army to a conventional army and defeat your enemy at their own game.

The reason to why I say it's deceptively easy is because there is never a 'one size fits all' theory that is going to work for every conflict. Those that do succeed adapt the theory to their local environment or add another dimension to it. The Viet Minh during the French Indochina War, for example, added the element of globalization through the use of engaging international opinion.

But not everyone has chosen to use Mao's theory for ideological reasons and sometimes, it is local conditions which makes it possible for a guerrilla force to win (or lose). The Cuban Revolution is a great example of this. With hindsight, it has quite a lot of pre-requisits which would be needed to wage a war according to Mao's theory: You had a society that was already contemptuous of Batista's regime. Castro and his band of guerrilla fighters were quick to gain the trust and support of the people who lived on the slopes of the Sierra Maestra which served as their safe haven and they also had a very (in literature overlooked) important resource in the urban members of the 26 July Movement who became vital in doing their part. With a very disorganized conscription army with low morale who committed several atrocities, it wasn't difficult to gain support from the people and even the armed forces themselves; they were promised to be well-treated and Castro kept to his word. The use of propaganda and in this case the radio through Radio Rebelde as well as the visits of international journalists engaged both the Cuban and the world opinion.

The Cuban Revolution was an astounding success and a man that saw this was Ernesto "Che" Guevara. The only problem was that he did not have the hindsight that we have today and completely misread the conflict. He created the foco theory based on his experiences in Cuba. The foco theory was based on the fact that it was the guerrillas themselves who would make the conflict possible. By their actions, they'd gain support instead of vice-versa: there was no preparation or political mobilisation of the masses. Thus, the guerrillas would the foco, the focus, of the conflict and lead the popular insurrection. The concept of separate political and military leadership also separated the theory from that of Mao's which stressed that of a unified leadership. As it came to be, Mao's theory worked much better in practice than Guevara's. Every movement that ended up using it failed, even as it was adapted for urban movements. Guevara's miscalculations and misreadings led to his own death in Bolivia 1967 where he was trying to create a popular insurrection through his own theory, to no avail.

These two examples are in my opinion very interesting and shows what can go right and what can go wrong in guerrilla warfare. It is the fusion of military means and politics which makes the guerrilla warfare of the 20th century 'modern' and which separates it from what came before.