Not big on my European history but at a guess:
100's of years ago the area was run by tribal or clan group(s).
Then squabbled over by various empires for a long, long time.
Then "taken in" by the Soviet Union.
Gained independence when the SU broke up.
The argument is over native Russians populating a part of Georgian territory who would prefer to live in Russia but don't want to move.
Oh...and throw in hundreds of years of mistrust and mistreatment on both sides, a Georgian govt who can't afford to cede territory, a Russian govt with aspirations of reforging an empire, etc.
But I'm just guessing:D

