The correct answer is: INDUSTRIALIZATION.
Industrialization succeeded due to the development of the factory production model, based on mechanization and technological progress and on generating output at a large scale.
While the agricultural sector had very low productivity levels and excess of workers, the industrial sector offered many job positions with comparatively more attractive salaries. Therefore people started to progressively move from the countryside (where most people used to work in agriculture) to cities, and the urbanization process had started.