International Criminal Court judges ordered an investigation of alleged crimes committed during the 2008 Georgian-Russian over the breakaway Georgian province of South Ossetia - the court's first investigation outside Africa.
The five-day war saw Russia strengthen its grip over largely pro-Russian South Ossetia, which had effectively been beyond Tbilisi's control since 1990. Russian troops pushed through South Ossetia deep into Georgia before withdrawing.
In a statement on Wednesday, judges said there was reason to believe crimes against humanity, including murder and the driving of Georgians from their homes, had been committed during the conflict, as well as war crimes including attacks on peacekeepers by Russian-backed South Ossetian and by Georgian forces.
The ICC, which has handed down just two convictions, of little-known Congolese warlords, has been criticised for bringing investigations only in Africa since being set up 13 years ago.
Last October, ICC prosecutor Fatou Bensouda asked to open an investigation after finding that up to 113 ethnic Georgian civilans had been killed and 18,500 driven from their homes as part of a "forcible displacement campaign" run by the authorities in mainly Russian-speaking South Ossetia.
Investigators will investigate allegations of crimes committed betweeen July 1 and October 10, 2008, covering periods either side of the five-day August war.
Opposing Georgian and South Ossetian forces appeared to have killed 12 peacekeepers, both Russian and Georgian, while Georgian forces had attacked a medical facility, Bensouda said.
The investigation pits Russia, a non-member of the ICC, against a strongly European-backed court at a time when east-west tensions are running high following Russia's 2014 annexation of Crimea and intervention in Syria last year.
The Hague-based ICC is already considering whether to open an investigation into crimes committed in Ukraine, another West-leaning former Soviet republic which is fighting Moscow-backed separatists in the east of the country.