

What you say of the Russian Empire and the contemporary Russian Republic regarding treatment of the Ukrainians is true, but it’s simply false when it comes to the USSR. The USSR defended Ukrainian sovereignty from the start, creating a Ukrainian republic with Ukrainian as the official language, a majority of publications in Ukrainian, right to an education in Ukrainian, and representation of Ukrainian politicians to the point of the USSR having as party leaders for the most part Ukrainians such as Khruschev or Brezhnev. Had it not been for the Soviets (including Ukrainian themselves), Ukraine would have turned into a genocided German colony in the 1940s according to Generalplan Ost, or at best many of its territories would still belong to Poland such as the city of Lviv.
Because associated independent preindustrial farms can’t face invasion from industrialized nations. Leaving the farmers in the past would have been the death of them. Remember: the USA, France, Poland, Japan, Greece, Estonia, Romania, Serbia and Italy invaded the RSFSR during the Russian Civil War for the sin of being communist. Stalin famously predicted the Nazi invasion 10 years in advance: