The tipping point for regime change arrives suddenly and is difficult to predict, even by those leading the revolution, as well as those leading the defense of the ruling regime. For example, at the time of regime collapse in Russia in 1917, Lenin was in Switzerland, Trotsky was in America, and Stalin was in Siberia. Like a dam that suddenly bursts as a result of the addition of a few more small drops of water, the exact moment of regime collapse is difficult to predict - even by leaders in the revolutionary movement and the forces defending the ruling regime. However, the destruction that follows the bursting of the dam is predictable. Three factors are proposed as preparing the ground for regime collapse. First, societal changes, which can be subtle, incremental, and long term. Second, changes in the ruling elite, particularly with respect to cohesion and fragmentation. Third, the emergence of a charismatic leader who takes charge of the revolutionary movement, often opportunistically putting themselves at the front of the movement.

The process of mutual radicalization is used as a framework to examine relations between the ruling regime and the revolutionary opposition. Mutual radicalization involves a collective process, in which rational individuals are overwhelmed by collective movements and behaviors, which are often irrational. During phase one, group mobilization takes place and the revolutionary opposition comes to perceive the ruling regime as distinct and different from the rest of society, illegitimate and immoral, unstable, and also an obstacle to future progress. During phase two, the ruling regime and the revolutionary opposition develop extreme ingroup cohesion in opposition to one another. Intergroup aggression and hostility increases. Individuals can step outside the group and recognize that the collective is behaving incorrectly, but social forces pressure rational individuals to conform to irrational collective behavior. In phase three, the identities of the ruling regime and the revolutionary opposition are reconstructed in opposition to one another. Each side defines themselves in opposition to the other group, and extremists control relationships between the two sides.

The much-feared event of Lorenzo’s death happened on 8 April 1492, heralded ominously by a bolt of lightning striking the cupola of the Duomo in the direction of the Medici palace.1 Piero’s years of apprenticeship were over and everyone awaited his response to the challenges ahead. ‘Who would Piero side with’, Parenti wondered, ‘and how would he be treated, as the boss, the equal or the inferior of the others?’2 Uncertainty about Piero’s reaction to the new, upside-down world that confronted him was widely shared, not least by Lorenzo’s secretary, ser Niccolò Michelozzi, who found himself isolated in Naples as his patron lay dying, consoled only by the letters he received from Florence.