In regards to both Ukraine and Georgia both were part of the Russian Empire prior to the Revolution of 1917. There was specific provinces or nations prior and these were the basis for the Republics of the Soviet Union. There was however the Civil War where the Red Army sought to keep the existing territories of the Russian Empire within the newly found Soviet Union. Therefore, it was more the preservation of the Russian Empire's territories and less forcing new lands into the fold. This however changed after the Second World War and the establishment of additional communist governments which were subservient to Moscow.

Most territories/states/countries did not join voluntarily. They were voluntold to be a part of the USSR. In some cases they were enveloped and absorbed into the USSR as one of the constituent federalist republics, in other cases they were simply kept on as 'independent' national states, such as Hungary, Poland or Czechoslovakia.

In the case of Ukraine, the Soviet mentality sort of derived from the Russian (imperialist), that is that the Ukrainians were not separate peoples with a separate ethnic heritage and identity, but rather were simply 'little Russians', and so were included, forcibly.