In times of conflict, societies are torn by being forced to choose between two opposing forces: the desire to make peace and the troubling possibility of making war instead. To resolve this tension, countries and peoples have striven for jus ad bellum, which generally means "just war" or "the right to wage war." This theory sets guidelines for declaring war, so that every conflict between countries will not devolve into military violence. Jus ad bellum recognizes that sometimes war is necessary, and it also recognizes that any war must only be undertaken with certain moral clauses considered. These moral clauses include matters relating mostly to the reasons and possible outcomes for a potential war.
One critical condition of jus ad bellum states that any war must have a just cause. In other words, armed conflict must not result from the wrong intentions. Imperialistic invasion represents one such wrongful intention. Most countries would consider self-defense or defense of allies as a valid example of a just cause.
A condition that war only be entered when all other peaceful measures have been exhausted constitutes another component of jus ad bellum. Mediation and economic sanctions are two common alternatives to a declaration of war. The United Nations Charter of 1945 sets forth war as an option of last resort.
Three other ideals comprise jus ad bellum: competent authority, cost-benefit analysis, and reasonable hope for success. The first ideal considers whether or not the individuals or groups declaring war have the authority to do so. For example, many countries may not recognize an alleged dictator’s declaration of war, whereas an accepted governmental authority may garner more support. War declarations should also weigh the gains of declaring war against the probable losses, namely financial loss and the loss of lives. In consideration of cost and benefits, involved parties should ascertain whether they have a reasonable chance at victory in armed conflict as well.
The 20th century witnessed several pacts and treaties between countries that provided legal definitions and foundations for jus ad bellum. The United Nations Charter put forth provisions condemning the use of force in conquering a recognized independent region for the purpose of making that region a territory of the invading party. This pact between numerous countries also advises that a subsequent war declaration be ratified by members of the UN. Two other multi-country pacts were instrumental in creating sanctions against aggressive, unjustified war as well: the Kellogg-Briand Pact of 1928 and the Nuremberg Charter of 1945. Generally, any official laws of war must be upheld by any military personnel or civilian who resides in the region.