A more thorough explanation:

Just war, also known as bellum justum, is a concept in international law and ethics that outlines the conditions under which a war can be considered just or morally acceptable. A just war is one that is fought for a just cause, with the right intention, as a last resort, with proportionality, and with a reasonable chance of success.

• The Allied Powers' fight against Nazi Germany in World War II is often considered a just war. The Allies were fighting to stop the genocide of millions of Jews and other minorities, and to prevent the spread of fascism and totalitarianism.
• The United States' invasion of Iraq in 2003 is a controversial example of a war that many argue was not just. The reasons for the invasion were based on faulty intelligence, and the war resulted in the deaths of hundreds of thousands of civilians.

These examples illustrate the importance of considering the justness of a war before engaging in it. A war fought for a just cause, with the right intention, and as a last resort can be morally acceptable. However, a war fought for unjust reasons or without proper consideration of the consequences can have devastating effects on innocent people.