Final answer:
The agreement by which countries agreed to treat prisoners of war in a decent way is known as the Geneva Convention, which includes treaties and protocols for the humane treatment of individuals during war.
Step-by-step explanation:
When countries agreed to treat prisoners of war in a decent way, it was called the Geneva Convention. The Geneva Conventions are a series of treaties and protocols that establish international law standards for humanitarian treatment during war. The treaties focus on the protection of non-combatants, wounded soldiers, and prisoners of war.
Among these, the fourth Geneva Convention treaty specifically outlines the humane treatment of prisoners of war and establishes a legal definition of war crimes. These conventions were a significant advancement in the laws of war, ensuring the ethical treatment of individuals during armed conflicts.