In leaving Britain, the early emigrants risked not merely their life savings but their very lives. Their voyages were never without hazard; their destinations were often unhealthy and inhospitable. To us, their decision to gamble everything on a one-way ticket seems baffling. Yet without millions of such tickets - some purchased voluntarily, some not - there could have been no British Empire. For the indispensible foundation of the Empire was mass migration: the biggest in human history. This Britannic exodus changed the world. It turned whole continents white.

Empire: How Britain Made the Modern World (2003)