Not only is it not a love song it is also not a song which is a "lament for the fallen Scots wiped out by an imperial power in greed for their land."
I'm afraid the truth is that the Scots in this instance were the aggressors and also somewhat foolishly the pawns in a European power struggle.

James IV (I think, I should check that but the story is the same regardless of which James..) was persuaded to invade England by the French Queen invoking the "Auld Alliance" at a time when the Scots and English were at relative peace; Border reiving in the Debatable Lands nothwithstanding.

The rationale from the French was that England would be too weak to fight a battle on two fronts simultaneously and that the Scots could therefore take the northern (still in parts, semi-Celtic) lands of Northumberland and Cumbria etc

The Scots marched off to battle and were wiped out at Flodden in Northumberland. The French decided not to get involved despite earlier promises of assistance if the "war" became a long one.
Most of the Scots nobility and the king (I'm sure now it was James IV) were killed in battle; and the majority of the Scots footsoldiers were similarly slaughtered, not mercilessly but in fighting.
Poor tactics against a superior force destroyed the Scots.

I am Scots and am proud to be so but on this occasion we were the aggressors not the victims.

andymac (apologies for the long comments but I like to try to get the facts right if possible.)