you almost have a point. El Salvador and Honduras have been getting along like two pattes in a Big Mac and the ceasefire between Moldova and Russia, who backed the Transnistria separatists, is as solid as a stale bap since MaccyDs set up shop in Chisinau.
However the Golden Arches couldn't prevent civil war breaking out in the former Yugoslavia, or in Nicaragua, and has had no political effect in the Lebanon. And, as far as I know, the Spanish have not given up their claim to Gibraltar, despite the presence of MaccyDs on the Rock.
However......as Branes points out Georgian and Russian troops most definitely fought over South Ossetia, (and, before that Abkhazia), and both sides refer to it as a 'war' even if no formal declaration of war was made by either. The Battle of Tshkinvali in 2008 involved artillery, T-72 tanks and strike aircraft, three of which were downed by anti-aircraft fire. I think it's worth noting that it took the French Government to broker the truce, and there is surely no greater criticism of MaccyDiplomacy than that.