Wikipedia
Zakerzonia (, Trans-Curzonia; ) is an informal name for the territories of Poland to the west of the Curzon Line which used to have sizeable Ukrainian populations, including significant Lemko, Bojko and Carpatho-Rusyn populations, before the invasion of Poland by the Soviet Union and Nazi Germany in 1939, and were claimed as ethnically Ukrainian territories by Ukrainian nationalists in the aftermath of World War II.
"Zakerzonia" stands for "territory beyond the Curzon line", or in Ukrainian "Zakerzons'kyi krai". About 700,000 Ukrainians or Ukrainian language speakers lived in Poland after World War II within the new borders. They were a "demographic majority in many areas along a long border strip running from Chełm almost to Kraków".
The Ukrainian Insurgent Army (UPA), at the height of their control of the territories, claimed plans of creation of Transcurzon Republic.
The demography of Zakerzonia drastically changed by forcible resettlement of the Ukrainians, with major undertakings being the expulsion of Ukrainians from Poland to the Soviet Union (1944-1946) and Operation Vistula (1947).