Amol Rajan explores how geology and demography have shaped the modern world. Paul Morland argues that we have underestimated the crucial impact of population changes on global events. He looks at how demography has had a major influence, from world wars to China’s rise; and from the Arab Spring to Brexit.

In the distant past people could walk all the way from continental Europe to England through the ancient region of Doggerland. Julia Blackburn scours the Suffolk coastline for this lost land which was submerged by rising sea levels around 5000 BC.

As the debate around the border between the Republic and Northern Ireland continues to dominate discussions on Brexit, the historian Diarmaid Ferriter explains how this line became a political battleground. The meandering boundary which cuts through fields and crosses rivers was once dotted with watchtowers and military checkpoints to stop movements of people and goods.

Producer: Katy Hickman