Ultimately, power in society boils down to the ability to influence people. We must not understand power only in its pejorative sense. Hitler had power and so did Mother Teresa. The most fundamental process involved in the creation and the projection of power is communication. One must exchange information with the individual(s) he wants to influence.
At the smallest scale, an individual can project physical power over another individual without having to communicate much, but here we are not concerned with individual-level physical power. At the societal level, the projection of military power, which is also a form of physical power, involves a lot of communication. The very fact that there is military power to be projected supposes some level of coordination and cooperation within that particular society, not only for the military act but also for military support systems. An army requires a sophisticated economy, central governance system and so on.
What if the means of communication change suddenly in a society? How would this affect power structures?
In the pre-Internet society, the most effective means of communication was one-to-many, like the radio, the television, the book, the newspaper, etc. It is a direct type of communication, in the sense that the message can reach the target, in one step. But these broadcast-type, one-way, one-to-many communication channels are usually very costly to create and to maintain. In order to sustain them, they require central governance, and over time they eventually become corrupted (not serving the interest of the masses) and get monopolized. These means of communication are, by nature, non-democratic, because they are not within the reach of every individual and have a strong tendency to get subverted and used against the masses. In fact, there is an abundance of examples where mass media was used by the social elites to increase their domination and to further their own agendas. That in itself is an indicator of how important information and communication is in building and projecting power.
The new digital technology introduced new channels of communication, in parallel with the classical direct one-to-many. The particularity of these new channels (now called social media channels like Facebook, Twitter, Youtube, etc. ) is that they are NOT direct. They propagate through the population from one individual to another. The process is very similar to word of mouth, but it is greatly enhanced by the new technology (larger scale, involving much more individuals, transcending geographical barriers, transcending language barriers, more dynamic). The fact that these new communication channels are NOT direct, are almost free, popular, and democratic changes everything. This means that the multitude has a lot more control over the narrative. Information doesn't follow along predefined paths as in a hierarchical social structure. It bounces around within decentralized online networks that individuals freely form. The dominant narrative emerges from this chaotic process, rather than being carefully crafted at the top of the pyramid and distributed down in a controlled and direct manner. In this new context the hierarchical power structure collapses because the information pathways it normally uses are no longer effective.
The elites have lost their monopoly on direct mass communication, people get their information from alternative sources, therefore the elites' ability to influence directly is greatly reduced. Moreover, they have also lost the ability to shapes preferences via values, norms, ideologies.