Final answer:
The Industrial Revolution, originating in Great Britain, was the pivotal event causing demographic and social upheavals. It led to urbanization due to agricultural changes and witnessed the catastrophic transatlantic slave trade. The era also embraced the Enlightenment and the Great Awakening, contributing to societal transformations.
Step-by-step explanation:
The event that led to massive demographic and social changes on both sides of the Atlantic was the Industrial Revolution. Originating in Great Britain, it brought sweeping transformations worldwide. The Industrial Revolution changed how people worked, traded, and traveled, influencing politics, economics, and social structures. Agriculture advancements facilitated by the enclosure movement led to increased yields but displaced peasants, causing a shift in population from rural to urban areas.
This period also included one of the largest migrations in history - the transatlantic slave trade. Europeans forcibly transported approximately twelve million Africans to the Americas, which altered the world demographically and culturally. The impact of this is still felt today through cultural innovations and the lasting scars of this human displacement.
Furthermore, the eighteenth century was marked by military expansion, the Great Awakening, and the Enlightenment. These movements revolutionized European colonial societies and the slave economy, leading to changes in consumer habits and intellectual thought, which further influenced social changes in global contexts, including the Americas.