We must first define Ethical and Moral Standards for Warfare.
For thousands of years, War was seen as a means to an end, the winner takes all, and a social consequence where the winner is allowed to loot and murder.
However, Abrahamic religions such as Islam, brought the concept of a proper code of conduct for Soldiers and rules on how to interact with an Army that had lost a war.
Today, in our modern world, the United Nations has its own charter and a governing body which oversees what it calls War Crimes and crimes against humanity.
The UN has a perfect set of charter and code of conduct which define the moral conduct that needs to be followed by soldiers nowadays.
However, after the United States use of torture in Iraq without any international pressure, it seems like not many nations are still willing to accept a globally codified war code of conduct.
By threatening a veto, the President can persuade legislators to alter the content of the bill to be more acceptable to the President. Congress can override a veto by passing the act by a two-thirds vote in both the House and the Senate. (Usually an act is passed with a simple majority.)
