Volhynia

Volhynia is a region of Ukraine that is located north of Podolia, south of Polesia, east of the Bug River, and west of Kyiv. Volhynia's area is about 70,000 square kilometers and its population is more than four million people.
Early history.
 In the 16th century, with the 1569 Treaty of Lublin, Volhynia became a largely self-governing part of the Polish-Lithuanian Commonwealth, keeping its Ukrainian character but having its elite become Polish, or Polonized. Most of Volhynia was annexed by the Russian Empire in the late 18th century due to the partitions of Poland. But Austria also got to annex a small part of Volhynia during this time.
19th century.
In the early 19th century, Volhynia was still dominated by its Polish nobility. They continued to rule over the Ukrainian peasants who lived there. Volhynia experienced a Russification program in the 19th century and did not get to experience the Ukrainian national awakening that was going on in neighboring Galicia during this time. 
20th century.
After the end of World War I, Volhynia was partitioned between Poland and the Soviet Union, with western Volhynia becoming a part of Poland and eastern Volhynia becoming a part of the Soviet Union, specifically a part of the Ukrainian SSR. Volhynia experienced a Ukrainianization movement in the 1920s but a lot of its notable Ukrainian intellectuals were later murdered in Joseph Stalin's Great Purge in the late 1930s. 
World War II.
In 1939, at the start of World War II, the Soviet Union conquered and annexed western Volhynia. It used to belong to Poland before that point in time. When Nazi Germany invaded the Soviet Union in Operation Barbarossa in 1941, Volhynia came under Nazi German rule for several years. Almost all of the Jews who were not evacuated by the Soviet Union ahead of time were murdered by the Nazis in the Holocaust. 
After WWII.
When the Soviet Union won World War II and got Volhynia back from the Nazis. Almost all of Volhynia's Germans and Czechs emigrated, in the former case to Germany and in the latter case to Czechoslovakia. In addition, after the end of World War II, a lot of the Poles in eastern Volhynia switched residences with the Ukrainians in western Volhynia. This made both eastern Volhynia and western Volhynia much more ethnically homogeneous. Volhynia also saw some Russians and Belarusians move there during the time that it was under Soviet rule. This increased the populations of these two groups in Volhynia. 
Statistics.
Volhynia was historically agricultural, with there being little industry there, especially in its western part. At the start of the 1930s, 78% of Volhynians worked in agriculture and only 8% in industry. In 1987, 52% of Volhynians still lived in rural areas, with most of these people still making a living based on agriculture during this time.