Complex sentence: Russia officially decided to intervene on 8 August, and sent units of the 58th Army and airborne troops across the Georgian border into South Ossetia, claiming to be defending both peacekeepers and South Ossetian civilians (who were Russian citizens).
Split into simpler sentences: Russia officially decided to intervene on 8 August, and sent units of the 58th Army and airborne troops across the Georgian border into South Ossetia. Russia stated it was defending both peacekeepers and South Ossetian civilians (who were Russian citizens).