Pāṇini sūtras

After su, sarva and ardha, the first vowel of the name of a country gets the Vṛiddhi, when a Taddhita affix with an indicatory ñ, ṇ or k follows.

1. su+sarva+ardhātसु+सर्व+अर्धात्

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	suसु	suसु	suसु	sस् + plus uउ
   sस्	sarvaसर्व	sarvaसर्व	sarva [word]	sarvaसर्व
   aअ	ardhaअर्ध	ardhātअर्धात्	ardha [word]	ardhअर्ध् + plus ātआत्

2. janapadasyaजनपदस्य

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   jज्	janapadaजनपद	janapadasyaजनपदस्य	country	janapadजनपद् + plus asyaअस्य

Anuvṛtti

1. uttara+padasyaउत्तर+पदस्य 7·3·10

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   uउ	uttaraउत्तर	uttaraउत्तर	following	uttarउत्तर् + plus aअ
   pप्	padaपद	padasyaपदस्य	word	padपद् + plus asyaअस्य