There have been poor countries and rich countries since countries first began, but only in the 20th century – the century of nationalisms and ethnic cleansings – have controls been implemented to stop movement between them. The argument for immigration controls stems from the belief, inherently xenophobic, that richer countries will be "flooded", "invaded", or "swamped" by "tidal wave" of migrants and that this will lead to increased unemployment amongst the native population. Quite simply, this is not true: overwhelmingly, unequivocally, the evidence supports the opposite thesis. According to Harris, immigration considerably enriches the host nation both scientifically and culturally. Immigrants do the jobs that most native workers do not want or cannot do. Without immigration our economies would dissolve. Nigel Harris shows exactly why and how immigration is the lifeline of the developed world’s economy, using examples from all over the world to prove how immigration makes both the rich and the poor richer and acts as the final safeguard against such ugly world phenomena as racism, nationalism, and intolerance.