[ux-app]

Off the top of my head I don't know of any one country that has a huge disparity (though I'm sure examples exist), but the EU is a good case study.

Legal Economic migration within the EU is definitely an issue, however it hasn't resulted in "destabilizing and draining the cities of resources".

E.g. Estonia's GDP is 99.07% smaller than the UK's[1], and Estonia is not empty. Edit - as pointed out below a per-capita comparison makes much more sense... oops

[1] http://www.wolframalpha.com/input/?i=estonia+gdp+vs+uk+

Edit: I know that GDP is not a measure of standard of living, but they are correlated and it servers as a reasonable proxy

[jsnell]

Raw GDP is an absurd proxy for standard of living, you're comparing a country of 70 million to a country of 1.5 million. At the very least you'd need it to be per capita. Maybe PPP adjusted.

[ux-app]

Thanks for pointing this out and you're absolutely right. The per capita comparison is much better, and shows Estonia's economy at 54% smaller [1] (Bulgaria makes for an even starker contrast at 82% smaller per capita [3])

Edit - As a final edit, the largest disparity across standard of living in the EU is between Luxembourg and Bulgaria, and comparing their per-capita GDP shows that Bulgaria's economy is 93.2% smaller [4]

This is still a considerable difference between the two countries and yet not everyone has fled from Estonia/Bulgaria.

The point though is that there is a very big spread in the standard of living [2] across the EU and yet mass migration is not occurring.

[1] - http://www.wolframalpha.com/input/?i=estonia+per+capita+gdp+...

[2] - http://www.theguardian.com/money/2014/dec/11/uk-living-stand...

[3] - http://www.wolframalpha.com/input/?i=bulgaria+per+capita+gdp...

[4] - http://www.wolframalpha.com/input/?i=bulgaria+per+capita+gdp...