Why hasn't the US Congress carried out the Department of Defense Law of War Manual in the Vietnam War?

If the United States Congress has carried out this Department of Defense Law of war manual in the Vietnam War. So, the United States Congress has been respecting loyalty, just cause, justice in the Vietnam War. However, the United States Congress not only distorted the American law and the US Constitution but also prejudiced the law of the department of defense law of war manual. Therefore, President Putin has been learned by heart from the United States Congress when Mr. Putin has invaded and subverted Ukraine's nation. But the United States of America has not helped Ukraine, the USA has advised President Ukraine must be left his nation when Mr. Putin could not invade Ukraine. As a result, the super strategist of Mr. Kissinger has not applied this Ukraine War. But Mr. Kissinger has applied for the Vietnam War. In fact, you want to study American law, you should study this Department of Defense Law of War Manual by the greatest power of America. Let you realize the settlement case of prisoner of war of Mr. Bright Quang.