Legal and illegal immigration of religious immigrants to European nations is a source of [[desecularization]] (see: [[European atheism and 21st century decline]] and [[Secular Europe]]).
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In many irreligious European countries, there is a sub-replacement level of births which is expected to cause challenges to their pension systems and labor supplies (see: [[Atheism and fertility rates]]).
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As irreligious populations rise in age, the fertility rates of these countries could drop further. The Rand Corporation indicates, "Nearly all European nations are experiencing long-term downtrends in fertility, and consequently, ageing of their populations. These demographic trends could have potentially damaging consequences for European economies."<ref>[http://www.rand.org/pubs/monographs/MG206.html Low Fertility and Population Ageing], Rand Corporation</ref>