Short answers, pulled from the story.
The crisis escalated in spring 2008 after Russia cancelled CIS economic sanctions it had imposed on Abkhazia in 1996, declared them outdated, and established direct relations with the separatist authorities in Abkhazia and South Ossetia. Russia explicitly linked these moves to Western recognition of Kosovo's independence.
The Bucharest summit in April 2008 was a major flashpoint. Russia sent a letter to the leaders of Abkhazia and South Ossetia on the same day the summit opened, addressing them as "presidents" and promising practical assistance. Russian diplomats and journalists at the summit said war in the Caucasus before December 2008 was inevitable following the announcement that Georgia's NATO membership would be considered that December.
On the 20th of April 2008, an unarmed Georgian UAV was shot down over the Abkhaz conflict zone. Georgia alleged a Russian MiG-29 from the Gudauta base was responsible. On the 26th of May 2008, the UN Observer Mission in Georgia confirmed, following an independent investigation, that the jet was Russian and that the Georgian video footage and radar data were authentic.
Russia deployed railroad troops on the 31st of May 2008, officially to repair a rail line in Abkhazia. By the 21st of July 2008, a 54-kilometer line between Sukhumi and Ochamchira had been completed. The repaired line was later used to transport military equipment for at least part of the 9,000 Russian soldiers who entered Georgia from Abkhazia during the August 2008 invasion.
On the 3rd of July 2008, a bombing killed South Ossetian police official Nodar Bibilov in the village of Dmenisi, and a separate bomb targeted pro-Georgian South Ossetian leader Dmitry Sanakoyev, wounding three of his bodyguards. By the morning of the 4th of July, South Ossetia reported three people dead and eleven wounded from fighting between Georgian and South Ossetian forces.
Russian military expert Pavel Felgenhauer wrote on the 20th of June 2008 that Putin had already decided to start a war against Georgia in late August 2008, predicting that provocations would begin in Abkhazia and South Ossetia before spreading. Robert Parsons had also written in May that war was becoming conceivable, citing Russia's ambition and Western diffidence.