The clue I believe is in the last verse. Hard by Loch Etive is the ruin of St Modan's Priory. Here, Robert the Bruce held the last Scots Parliament ever conducted in Gaelic. At KilChrenan (also in Oban, as is Loch Etive) Cailean Mór Caimbeul, one of the earliest attested members of Clan Campbell, is buried. He met his death at the battle of the Red Ford. Cailean Mor, previously a staunch supporter of the Bruces (not the famous Robert but his father before him), had allied himself with John Balliol - a disputed "king" in the interregnum following the death of the Maid of Norway. Balliol (rudely called Toom Tabard or empty shirt by opponents) held his position with the support of Edward I of England. Edward gave the Campbells the title of "Ballie" of Loch Awe, which pissed off the MacDougalls of Lorne, to whom it had previously belonged.

Hence the battle, but also two places important just prior to what are called the Wars of Scottish Independence, wars which saw Scotland - which retained its independence - left shattered economically, owing an enormous ransom to England (that never did get paid) and with the Stone of Scone - the sacred stone on which the Kings of the Scots were crowned - in English hands. The Scots were still at war internally, and would pretty much remain so for a good long while.

So while I think the song also references modern day Scotland, it has a long base in history, something Dougie Maclean is very familiar with