Activation occurs first at the individual level, then at the collective level, and finally at the planetary level. The global activation process is visually illustrated in the Great Invocation meditation/visualization.
Under healthy global and social conditions (i.e. conditions filled with love, support, prosperity, grace, and guidance), activation occurs as a normal and safe part of the Development process. Under healthy conditions, activation occurs when the energy systems of the physical unit (including the seven main chakras) mature and become fully active. Under unhealthy conditions, activation must be preceded by Healing.
Current planetary conditions are not healthy. Currently we live with a Toxic Socialization process designed to prevent activation while at the same time propping up a destructive and venal System. The Toxic Socialization process is designed to suppress Consciousness (i.e. lower Consciousness Quotient) and distort and destroy the energy systems of the body in order to prevent activation. Therefore under current conditions activation often requires conscious, and possibility therapeutic, intervention.
Activation -> Chakras
Sharp, Michael (GA). The Great Awakening: Concepts and Techniques for Successful Spiritual Practice.