Sher,

You wrote ‘No one wanted to invade Western Europe, because till the 17th century it was too poor.’ Tell that to the Ottoman Turks who started invading Europe in the 15th century and the Arabs before them.

And again, ‘The same reason people only emigrated from Europe till the 20th century.’ By the 1800s, Europe was richer than either China or India thanks to the Industrial Revolution. As a result of increases in population, Europeans left by the millions to settle, and develop, vast lands in the Americas and Oceania, that Europe opened up. Today’s North America, Latin America, Australia, New Zealand are the result of this huge migration of about 40 million Europeans.