in modern international relations, leaders are not legally required to provide a formal, advance explanation to each other before going to war, and explicit declarations of war have become very rare.
While historical, chivalric, or legalistic traditions—such as the Hague Convention (III) of 1907—once dictated that nations issue formal warnings or ultimatums, this is no longer the standard practice.
Oxford Public International Law +1
Here is the breakdown of why and how this works:
- The End of Formal Declarations: The last time the United States Congress formally declared war was World War II, despite engaging in numerous conflicts since. Modern conflicts often begin with surprise attacks, "special operations," or undeclared, de-facto hostilities.
- Strategic Surprise: Attacking nations usually want the benefit of choosing the time and place of the assault, making a "heads-up" counterproductive to their military objectives.
- Legal Standing: While a formal declaration is not necessary, international law (under the UN Charter) generally prohibits the use of force unless it is in self-defense or authorized by the UN Security Council.
- Euphemistic Language: Instead of declaring war, leaders often frame military action as "self-defense," "intervention," or "special military operations" to avoid legal or international backlash.
- Notifications: While not a "courtesy" announcement, international law requires that if a state of war is acknowledged, it must be officially declared to avoid confusion, and parties to conflict are required to adhere to international humanitarian law (laws of war) regardless of whether a declaration was made.
Wikipedia +4
In summary, while leaders might explain their actions to the world or to their own people for propaganda or legal justification, they rarely provide formal notice to their adversary beforehand.
