In early literature a battle between a red and white dragon has symbolised struggles and wars between the inhabitants of this island. Later interpretations have often considered the red dragon to represent the Celtic Welsh (and has been adopted in the Welsh flag), with the white dragon representing the Anglo-Saxon English.
From Nennius' Historia Brittonum circa 828:
I will now unfold to you the meaning of this mystery. The pool is the emblem of this world, and the tent that of your kingdom: the two serpents are two dragons; the red serpent is your dragon, but the white serpent is the dragon of the people who occupy several provinces and districts of Britain, even almost from sea to sea: at length, however, our people shall rise and drive away the Saxon race from beyond the sea, whence they originally came; but do you depart from this place, where you are not permitted to erect a citadel; I, to whom fate has allotted this mansion, shall remain here; whilst to you it is incumbent to seek other provinces, where you may build a fortress.
From Geoffrey of Monmouth's fictional work Historia Regum Britanniae, 1136:
Woe to the red dragon, for his banishment hasteneth on. His lurking holes shall be seized by the white dragon, which signifies the Saxons whom you invited over; but the red denotes the British nation, which shall be oppressed by the white. Therefore shall its mountains be levelled as the valleys, and the rivers of the valleys shall run with blood.