Its the breakthroughs in technology that are relevant in their time to disrupt the status quo.

Roman Roads allowed Legions to march and counter-march about the empire; and connected disparate populaces in unprecedented ways. All roads led to Rome, and the Barbarians followed them there...

Gutenberg invents a printing press, and a European populace controlled through ignorance and the Catholic Church was able to soon read, write and think for themselves; and those with political agendas soon recognized the power in Luther's work and converted it to their purpose. Within 200 years Western Europeans had developed the concept of the modern nation-state and had leveraged associated breakthroughs in technology to conquer and dominate the globe. The Holy Roman Empire faded from the scene.

A global grid of telegraph cables allowed Britain to dominate the second half of the 19th Century; but as populaces read of revolts in one corner of the empire in their own corner a day later, the costs of controlling such a vast empire soon came to exceed the benefit. Information could be everywhere at once, but the Army still moved at the speed of horse and steam.

The Soviets dominated post-WWII Eastern Europe, but could not control the information flowing from Satellites into the homes of the populaces they sought to divide, suppress and exploit. It shocked the world when those populaces so empowered rose up in a wave the Soviets declined to put down.

Following collapse of the Soviets tensions among the many populaces of the Middle East began to slowly build. Western manipulations of legitimacy and sovereignty of governance to contain the Soviets were benign in comparison, but faced increasing resistance as they shifted from being "the lesser of two evils" to simply being "the evil." Cellular phones, wireless Internet, social media all served to not only share grievances and motivation, but also allowed savvy insurgents to develop new tactics of networked operations and provided the ability to skip the time-honored (and highly vulnerable and dangerous) organization phase of insurgency. "Flash Mobs" and instantaneous and continuous global news cycle quickly put tired and despotic regimes on their back foot, and left Western powers in shock as their carefully crafted schemes of influence and manipulation began to unravel.

Over the years, these breakthroughs always precede change where change is needed. An associated shift of sovereignty being vested in one man, one family or one class and a trend to distribute it back across the people follows. Such changes are typically resisted, and almost always slow and messy. They are also unstoppable.