In 2008, Russia and Georgia went to war for five days over South Ossetia. The conflict remains unresolved as Russia builds what it calls a new international border between this breakaway region--the so-called "Republic of South Ossetia"--and Georgia.
South Ossetia, a region roughly the size of Rhode Island with a population of some 40,000 ethnic Ossetians, declared its independence from Georgia in 1990, following the breakup of the Soviet Union. After a two-year war and an imperfect ceasefire, South Ossetia operated for nearly two decades as a self-declared independent state, with periodic flare-ups in fighting.
The region had its own government, but no enforced border. That changed in 2008.
In August of that year, Georgia launched an offensive to retake control of the breakaway region. In a war that lasted five days, Russia responded by invading and occupying South Ossetia. Then it recognized it as a sovereign state. Most of the rest of the world, including the United States and Europe, declined to follow suit. The only other countries that recognize South Ossetia are Nicaragua, Venezuela and Nauru.
Since then, despite a tenuous peace, the conflict remains unresolved, as Russia has slowly been turning the previously theoretical borders of South Ossetia into real lines on the ground.