The Red Cross on White Background originally associated with far back as the crusades ear, It was only until after the end of the Third Crusade when the emblem became recognised as the Cross of St George, known as the Warrior Saint.
King Henry II of England went on a crusade in 1188 and used the white cross on a red background, however, this design was later reversed into a Red Cross and white background, which distinguished mark worn by English Soldiers from the Reign of Edward I.
Saint George had become popular as a “warrior saint” during the crusades and Edward III, who in thanks for Saint George’s supposed intervention in his favour at the Battle of Crécy gave him a special position as a patron saint of the Order of the Garter in 1348.
St. George finally rose to the position of the primary patron saint of England during the English Reformation when all religious flags, including all saints’ banners except for his were abolished.
In 1606, after the Union of the Crowns in 1603, it was combined with the Scottish St Andrew’s Cross to form the Union Jack, which James VI & I ordered be flown from the main tops of ships from both England and Scotland.