Damn what is up with Poles spreading across the world? Hell there even some in Haiti and Martinique that are of Polish descent.
We had major emigration periods mostly after failed wars/uprisings. First one took place after 1830 when like million people went to France mostly. This happened after November Uprising.
In 1863 after January Uprising another mass of people migrated.
A lot of people moved to USA in early 1900s. Then after WW2 shitloads of people, mostly fighting on Western fronts, would rather stay in UK and other countries than move to Communist Poland, where they would most likely get killed anyway.
And of course people were running away during the whole communist period.
This happens when your country has a terrible location between Germany and Russia.