Polish immigration to the United States occurred in three major waves:
The first wave of immigrants, arriving mainly from the late 1800s up to the WW I, were considered "za chlebem" (means "for bread") immigrants. They came to America mainly from economical but also political and religious reasons. Many immigrants were illiterate and unskilled laborers in their own country. The majority came from South and Southeastern part of Poland (Carpathian and Tatra Mountains, Krakow and Rzeszow area). These areas were very poor and overpopulated until the beginnings of XX century when tourism industry started developing. This first and large group of immigrants is difficult to account for since they came from Poland when Poland did not exist as a separate country but was partitioned between Prussia, Russia and Austria. So they were registered as citizens of these countries rather than Poland.
"These immigrants took low-paying jobs and lived in crowded dwellings just to make a meager living."(Ref. 1) Also many Jews from Eastern Europe came in this time. Among Jews very few were coming back to their country of origin much less than among Poles who sometimes came to America to earn some money and were ready to go back to their old country.
The second wave of immigration took place after World War II. During the war, Poland lost disproportionally more people than any other country. Over 6 million of its 35 million people were killed. Poland was also devastated economically, many towns and businesses very destroyed. The fact that Poland was liberated by Soviets and consequently turned into communistic country posed a danger for Poles who from different reasons were still abroad or were fighting along Western aliens during the war. "Individuals in this second wave were primarily political prisoners, dissidents, and intellectuals from refugee camps all over Europe. Many in this group, who were educated and committed to assimilating into American culture, separated from Polonia and aligned themselves with other middle-class and professional groups in America. The upwardly mobile and middle-class aspirations of this group differed from the working-class orientation of the first- and second-generation descendants of the first wave." (Ref. 1)
The third wave of immigrants started arriving in 1980. The first immigrants came after the martial law in December 1981. Some won visa on the visa lottery. Some immigrants of the newest wave are very skilled professionals. Quite numerous group of faculty in American universities consist of good educated Polish immigrants of the newest wave. Some, especially illegal immigrants are not still that well settled down in the society and they live in low-income housing mainly in Polish quarters in Chicago, New York or Detroit.
In early 80-es the value of Polish currency (zloty) was very low compared to dollars. Thus Polish immigrants of newest generation tried to save as much as possible. They even tend to save money on food by eating nutritionally inadequate diets and not seeking health care until a problem becomes severe. Right now the Polish currency is more stable and all the important products are available on the Polish market. This allows the new immigrants to live more normal and stable life. For illegal immigrants - networking with other Poles is their primary source of job contacts. Because many of these new arrivals have been used by inscrutable Poles and others, many are terrified of strangers and bureaucrats who may have them deported if they are found working.
The number of Americans of Polish descend is about 10 millions, but the number of the illegal Polish immigrants is also high, 70 thousands and it ranks us in the 10th place in the USA. This is one of the reasons why it is so difficult to receive a visa to the USA for an average Pole.