Across the globe, immigration is politics. The issue dominated the last years of the Bush Presidency, and is now a prominent item on President Obama’s agenda. In the US, Canada, UK and Continental Europe, many fear that immigration systems will be abused by radical jihadists intent on launching terrorist attacks. And across the West, with the sole exception of Canada, the majority of the citizenry wants fewer immigrants. In the last few days alone, the European Parliament adopted a major asylum bill; Italy controversially sent two hundred boat people back to Libya, and President Obama announced a major increase in spending on border control.

Immigration is by no means an exclusively Western phenomenon. Russia, China, Malaysia, and the Middle East are all home to tens of thousands of migrants, and many more pass through these and other countries on their way to the West. No country, in short, is a non-immigration country, and every country has its own politics of immigration or emigration.

It cannot be any other way. Each year, hundreds of thousands of people flee poverty and persecution and seek wealth and stability. Some travel with authorization, but most travel illegally, relying on smugglers (to whom they pay for passage from point A to B) and traffickers (to whom they remain indebted after they arrive, often living as no more than indentured servants). For the South (understood as migrant-sending countries), immigration is a necessary mechanism for coping with high population growth. For the North (understood as migrant-receiving countries), immigration fills sector-specific labour shortages (say, in the high-tech sector).

The problem, however, is that the immigrants that the South wants to send are not typically the ones that the North wants to receive. The South wants to encourage the mass emigration of the unskilled workers filling its overpopulated cities, while retaining high-skilled professionals and entrepreneurs. The North wants exactly the opposite.

This is not a problem that is going to go away. Over the next four decades, world population is expected to grow from 6.79 billion to 9.2 billion (peaking at that level in 2050). Over 80 percent of that growth will be in the world’s poorest regions: Africa, Asia, and Latin America (in that order), almost exclusively by way of reproduction. European populations, by contrast, will decline, and those in North America will grow only slowly. The result, by the middle decades of this century, will be a drastic population imbalance: stagnant, ageing, and often declining Northern populations versus large, growing and young Southern populations.

If the rich North shuts its doors to these Southern populations, then the best-case result will be a great surge in illegal migration northward (most of it trafficked, with all the attendant human misery) and the militarization of Northern borders. In the worst case, population growth will obliterate economic growth in the South, wreck social structures, and lead to war. If it does, the chaos will not be confined to the South. Economic disruptions will reduce wealth in the North; migration-related crime (above all, trafficking) will surge; and those manning (and arming) borders may face the choice between firing on illegal migrants and allowing them to pass. The latter scenario was suggested as far back as 1973 in Jean Raspail’s possibly hysterical, possible prescient Camp of Saints.

Those wishing to reject these pessimistic predictions make one simple but powerful argument: the North needs immigrants. The Wall Street Journal, The Economist, international organizations such as the UN and the ILO, as well as some Western governments, have repeatedly claimed that the North’s wealth depends on immigration. It does not. Once the full cost of immigration (health, welfare and infrastructure spending) is subtracted from the benefits (taxes paid, goods purchased and produced), the net positive impact of immigration is miniscule. In 1997, the US Commission on Immigration Reform (a bipartisan, expert commission appointed by Congress in 1990 to look into all aspects of immigration to the US) estimated the net economic benefit of immigration to the US at between $1 billion and $10 billion per year (or one-tenth of one percent of GDP). In an economy this size, the larger figure is the equivalent of two weeks’ economic growth. Put another way, the entire yearly benefit of immigration to the US could be matched or exceeded by working 30 minutes more each day (or skipping the coffee breaks). Such economic benefits are higher when migrants’ skill sets differ from those of domestic workers (unskilled workers complement and raise the real wages of skilled workers; skilled workers can increase the competitiveness of the economy), and indeed lower when there are negative externalities (crime, congestion, overcrowded schools).

People often think that North American economic growth only occurs when there are high levels of immigration (a correlation, if not a causation). This, too, is false: the US experienced decades of great prosperity (the 1920s, 1950s and part of the 1960s) with almost no immigration. In 2008, the House of Lords Select Committee on Immigration reached essentially the same conclusion for the UK. The overwhelming benefit of immigration accrues to the immigrant, not the receiving country. Whatever immigration does, it does not make rich countries rich.

Given this fact, is there still an argument in favour of large-scale immigration? There is, and it rests on two claims. First, evidence from the last 20 years suggests that mass immigration will likely occur no matter what the North does. Throughout the 1990s, the US had an official policy of zero illegal immigration; each year, some 500,000 such migrants arrived. Second, the costs of not allowing the South an outlet for relieving population pressure would simply be too great. If mass immigration is going to occur, or if it is unthinkable not to let it occur, it is in the North’s interest to do what it can to make immigration work.

What does this mean in practice? Political theorists and immigration activists argue that the North needs open borders and open hearts: mass immigration should be linked with generous welfare states and high wages. Unfortunately, they live in a world of free lunches. In the context of high fixed wages and/or generous social security, high levels of unskilled immigration must lead to mass unemployment and a concomitantly abrupt effort to end same immigration (in view of the fiscal strain and likely political opposition). Channelling immigrants into work is therefore essential: immigration works where immigrants work.

More broadly, immigration choices are inevitably shaped by what labour economist Phil Martin calls the rights/numbers tradeoff: the more rights (to unionization, generous social security, high wages) a rich country offers, the fewer immigrants it can admit, and vice versa. Ten migrants can be given Mercedes and mansions; ten million cannot. If the North is to cope with large, unskilled immigration, its governments will need to liberalize labour markets (allowing wages to follow) and reform welfare states (reducing income support in periods of unemployment).

The developments I am describing here – lower wages and fewer rights – may not be appealing, but they inevitably flow from wealth and population imbalances that will worsen over the next decades. More positively, they will also bring individual benefits. High-earning, overworked, two-income families in the North will have a ready supply of cheap labour; workers from the South will have a life that, if not great, is at least better than the one they left behind. And, above all, more than a handful of Southern migrants will be able to enjoy it. The alternative – futile attempts to limit immigration, the transformation of borders into battlefields, and appalling social and economic instability in the South – is far worse.

Randall Hansen is a professor of political science at the University of Toronto. He holds a Canada Research Chair and specializes in political history and public policy. His most recent book is Fire and Fury: The Allied Bombing of Germany, 1942-1945 (2008), and he is preparing a co-authored study on the history of eugenics, forced sterilization and population control.