How does this fit into the bigger picture?

Grotius on the law of war and peace

In 1625, in response to the horrors of the ongoing Dutch War of Independence with Spain (1568-1648) and the Thirty Years War, the Dutch lawyer and philosopher, Huig de Groot (better known now as Hugo Grotius) wrote De Jure Belli Ac Pacis (“On the law of war and peace”).  

In Part 3 of this book he addressed the rules which he believed should govern the conduct of a war once it had begun. It covers such issues as the killing of enemies, the treatment of prisoners, pillaging, the acquisition of territories, the treatment of neutrals, truces and safe conduct, terms of surrender and the negotiation of peace treaties.

Grotius’ thinking influenced the drafting of the peace treaty, the Treaty of Westphalia, which finally brought the Thirty Years War to an end.