Ponniyin selvan is such a great epic in the genre of novels based on history,each and every incident in that novel has its own importance and even we can say that each and every incident determines the proceeding events.
i can give u lot of examples like saving the life of vandhiya devan and ponniyin selvan by poonguzhali,kunthavai teasing nandhini in their childhood and many events,even though they seems to be trivial,they gets the important part in the story some way.
so,most important turning point in the PS is that "THE DEATH OF VEERA PANDIYAN IN THE HANDS OF AADHITHA KARIKALAN" because it makes the nandhini to take vengence on AK and make her to take a oath to destroy the chola vamsa.
i will list out the reasons why this event is the most important one,
1.if veera pandiyan is not killed by AK,then there is no reason for nandhini to take revenge on AK. 2.also,the murder of AK wont be happened in the history. 3.nandhini wont get married to Periya pazhuvattariyar and PP wont called for sathiyalosanai to make madhranthaga as king. 4.to the crown of all i said before ,ponniyin selvan wont be the king because aadhitha karikalan is there alive.the whole chozha history will be changed in to a different one if veera pandiyan is not killed by the angry but courageous AK.
so,i strongly beleive "THE DEATH OF VP IN THE HANDS OF AK "is the most important turning point.
this my view.all u replies and ur opinions r welcome.
Veerapandiyan getting killed by adityakarikalan in the presence of Nandhini
Think about it no nandhi there AK kills VP comes back to the king and asks for her hand in marraige and the king agrees you have a greatest warrior who is so happy that they rule and live happily everafter...
Nandhini was the key there She mad AK mad and go into self banished exile in Kanchi...that agreived the sittrarasargal and made them choose Maduranthagan that agreived Kundavai and she nurture Arulmozhi....