My pet theory is that the beginning of the idea of a nation start with Louise de Savoie. The intrigues she ran harshly reduced the power of dukes while giving the royal domain and it's merchants a lot of power. The narratives the French crown drew around itself and its power helped, and the consolidated territories, removing a lot of enclaves and foreign vassals (things other crowns started to do too) was to me the beginning of the 'territorial integrity' idea.

And it's only her second biggest achievement.