What union policy change spelled extermination for the prisoners in the andersonville prison camp?

The infamous Andersonville Prison Camp housed around 45,000 Union prisoners during the U.S Civil War, which is four times its capacity. Although the prison camp became infamous for prisoner deaths due to poor sanitation, little rations, and overcrowding, there is no evidence to date suggesting that the Confederacy meant to exterminate prisoners. The Confederacy can’t even provide sufficient food, clothing, and medical care for its soldiers. They even tried to offer a conditional release to the prisoners.

it provided for equal trade rights among nations in china.