Math As a lasting effect of the Famine, which itself was a result of rigid adherence to to the demands of the dogma of free market Liberalism, Ireland is the only country in Europe that has today a far smaller population than it had 150 years ago.
While not technically true, countries with decreasing populations is on its own rather interesting, although without sticking to your 150 year time period.
Pretty much all of the former Eastern bloc countries have experienced population decline, mainly due to outward migration and falling birth rates. So to be cynical, you could argue that the Soviets made such a mess of those countries under communism, that people couldn't wait to escape to the capitalist west once they had the chance. The Soviets also destroyed much ethnic and non-Russian culture, and many of those non-ethnically Russian regimes are now depopulated, as their people tend to move to the cities.
Some examples: Albania had 3.2 million people in just 1989. It now has just under 2.9. Armenia has had a near 20% reduction in 25 years. Bulgaria and Latvia are the only countries in the world to have a smaller population today than 1950. Bulgaria has lost nearly 25%, down from 9 million in 2001 to 7.3 million and falling. Latvia has lost 34.3% since it was freed from Soviet control, Estonia 19.2% and Lithuania 23%.
Ireland's population reached a peak of 8 million in the 1800s but fell to 2.8 million in 1961. However, it has now reached 4.58 million since then, under those damned Western capitalist policies.
Being cynical, you can argue that Germany can very well afford to be open to the current migration crisis as it does not have an increasing population in the same way as that vile capitalist state, the United Kingdom.
So in terms of that very simple and very human measurement of people voting with their feet, of getting out of a country when they can get out and so on, it does seem that the western capitalist countries are definitely the most popular, and that current and former Communist countries are just not very popular places for the majority to live in (unless exit is prevented by the State and access to information about other countries severely restricted and reinforced by propaganda).