Lenin's attempts to assuage Ukrainian nationalism through a measure of cultural autonomy were abandoned by Stalin, who also imposed agricultural collectivization on Ukraine and requisitioned all grain for export. Millions of Ukrainians died in the resulting famine. Mykola Skrypnyk and other Ukrainian Communist leaders who opposed Stalinist measures were purged and executed. During World War II, many Ukrainians at first welcomed the Germans as liberators and collaborated with them against the USSR. However, the Nazis' scorn for all Slavs and their harsh occupation (1941–44) of Ukraine turned many Ukrainians into anti-German guerrilla fighters.
The republic suffered severe wartime devastation, esp. as a battleground both in 1941–42 (the German advance) and 1943–44 (the Russian advance). Most of Ukraine's 1.5 million Jews were killed by the Nazis during the war; many were shot outright in 1941, at such sites as Babi Yar. Several major territorial changes occurred in Ukraine during this period. South Bessarabia, recovered from Romania in 1940, was incorporated into Ukraine, while the former Moldavian ASSR was detached from the republic and merged with central Bessarabia as the Moldavian SSR. The northern parts of Bukovina and Bessarabia were added to Ukraine, as was E Galicia, including Lviv, formally ceded by Poland in 1945. Transcarpathian Region, which had been part of Czechoslovakia since 1919, was also ceded in 1945, thus completing the process by which all Ukrainian lands were united into a single republic. Crimea was annexed to Ukraine in 1954. Although Russification intensified in Ukraine (as in other Soviet republics) after World War II, Ukrainian nationalism remained strong.
During the 1960s, Ukrainians emerged as tacit junior partners of the Russians in governing the Soviet Union. Leonid Brezhnev was born in Ukraine and held important party posts there before being called to Moscow. Former Soviet ruler Nikita Khrushchev, although a Russian by birth, served as first secretary of the Ukrainian Communist party during the 1930s and carried out the Stalinist purges in Ukraine. In 1986 one of the reactors of the Chernobyl nuclear power station exploded, contaminating a wide area of Ukraine.
