https://hindupost.in/history/heroic-hindu-resistance-to-muslim-invaders-636-ad-to-1206-ad-by-sita-ram-goel-chapter-6-the-nature-of-national-frontiers/
‘Heroic Hindu Resistance to Muslim Invaders (636 AD to 1206 AD)’ by Sita Ram Goel – Chapter 6: The Nature Of National Frontiers