The Soviet Union is pretty common knowledge. But most of the time the U in USSR is skipped over. After all, why would the Russian Empire break up just to be reunited? Let's find out.
Moldova (Since I forgot it): Moldova was a region on the border of Ukraine and Romania, and because of that, Romania had a Moldova province and Ukraine had a Moldovan Province. With the Molotov-Ribbentrop Pact, Romania was in the Soviet Sphere. The Soviets then took Romanian Moldova and merged it with Ukrainian Moldova and gave in SSR status.