In India, specifically for the UPSC Civil Services Examination (Political Science & International Relations optional) and UGC NET, World Constitution by Vishnoo Bhagwan is often recommended reading.
While many scholars have written on individual national constitutions (USA, UK, Russia), Bhagwan’s work on World Constitutions is unique because he frequently tied individual state structures back to the larger, idealistic framework of a —a legal and political authority above nation-states. world constitution vishnoo bhagwan pdf