Jus ad bellum is a set of criteria used to determine whether entering into war is justified. It focuses on the reasons for going to war, emphasizing that a state must have a legitimate cause, such as self-defense or protecting human rights. The principles aim to prevent unnecessary conflicts and ensure that war is a last resort. Additionally, jus ad bellum includes considerations like proportionality and the likelihood of success. These criteria help assess whether the benefits of going to war outweigh the potential harms, guiding nations in making ethical decisions about military engagement.