Short answers, pulled from the story.
Kresy is the Polish plural of kres, meaning "edge" or "border." According to Zbigniew Gołąb, it derives from a medieval borrowing from a German word meaning borderline or circumscribed territory. The word first appeared in Polish literature in Wincenty Pol's 1854 poem "Mohort," where Pol defined Kresy as the line between the Dniester and Dnieper rivers near the Tatar borderland.
Kresy amounted to nearly half the territory of interwar Poland. As many as 12 million inhabitants lived in the Eastern Borderlands, with ethnic Poles making up only about a third of the population and Ukrainians comprising another third. Most small towns in the region were shtetls, reflecting the large Jewish presence across the area.
Between 1944 and 1946, more than a million Poles from Kresy were moved to the Recovered Territories in western Poland, including 618,200 from Eastern Galicia, 226,300 from Polesia, 150,000 from the area of Wilno, and 133,900 from Volhynia. A second mass repatriation took place between 1955 and 1959. In total, over two million Polish people left Kresy between 1945 and 1960.
Kresy was the birthplace of Adam Mickiewicz (born in Zaosie, now Belarus), Juliusz Słowacki (born in Krzemieniec, now Ukraine), Czesław Miłosz (born in Seteniai, now Lithuania), Joseph Conrad (born in Berdychiv, now Ukraine), and Ignacy Jan Paderewski (born in the village of Kurilovka, now Ukraine). Tadeusz Kościuszko, national hero of Poland, Lithuania, the United States and Belarus, was also born in the region, in the village of Mereczowszczyzna in current Belarus.
The Pale of Settlement was a scheme devised by Catherine II of Russia to restrict where Jews could settle, keeping them from the Orthodox Christian core of the empire including Moscow and Saint Petersburg. It was established after the Second Partition of Poland and lasted until the Russian Revolution in 1917. Kresy is largely co-terminous with the northern areas of the Pale; together they held a Jewish population of over five million, representing 40% of the world Jewish population at that time.
A survey conducted in early 2012 by the Centre for Public Opinion Research found that almost 15% of the population of Poland - between 4.3 and 4.6 million people - declared that they were born in Kresy or had a parent or grandparent from the region. In Lubusz Voivodeship, 51% of inhabitants reported family ties to Kresy; in Lower Silesian Voivodeship, the figure was 47%.