to seize Georgia's northern territories.
By the way, it was recognized by foreign countries as georgian territories, but they really should become an independent states at the moment of decomposition of USSR (by laws that was active in that moment - autonomous republics within one of 15 republics that is planned to separate had the right to decide - should they remain as autonomy in that republic, or become new subject of USSR). For example, Abkhaz autonomous republic had referendum, that was willfully boycotted by ethnic Georgians so only Abkhaz people participated and they decided to keep Abkhazia as a subject of USSR. Almost at same time Georgian part of Abkhaz ASSR population participated in georgian referendum - that was about independency. That one, in turn, was boycotted by Abkhaz population.
So, real status of this two autonomies was not so clear from beginning. And once Kosovo precedent destroyed principle of invariance of borders, georgians had no way, except force like with now not existing Adjaria, to keep this de-facto independent autonomies.
What to South Ossetia - it was included to Georgian SSR purely by administrative reasons. Before tunnel was built, there was problem to get from southern part to northen part during winter. So, Ossetia was split to two autonomies separated by Caucasus mountains - one withhin RSFSR, another within Georgian SSR.
Just like Crimea that was handed to Ukrainian SSR from RSFSR by Khruschev due to complicated administration of area that was separated by water from RSFSR. By the way, also, that "movement" was in fact illegal according to laws that was in effect that time.