Complex sentence: It is viewed by many as Scotland's "alternative" national anthem (although there is no "official" Scottish anthem), though Henderson felt that part of its strength lies in the fact that it is an alternative, "International Anthem".
Split into simpler sentences: It is viewed by many as Scotland's' alternative'national anthem (although there is no' official' Scottish anthem). However, Henderson rather felt that part of its strength lies in the fact that it is an alternative, an "International Anthem".