Who made the just war theory?

The just war theory has its roots in ancient philosophical and religious thought, but it was notably developed by St. Augustine in the 4th century and further refined by St. Thomas Aquinas in the 13th century. Augustine emphasized the moral justification for war, while Aquinas provided a systematic framework outlining the conditions under which war could be considered just. Over the centuries, various scholars and theologians have contributed to the theory, but Augustine and Aquinas remain its foundational figures.