The Catholic principles of the just war are as valid today as ever they were, so it was heartening that the pope has reiterated their importance. In a conversation with journalists following his trip to Kazakhstan, he declared that the purchase of weapons can be “morally acceptable if done under the conditions of morality”. Those conditions must be understood in the terms articulated by St Thomas Aquinas and expanded by others, namely, a war must be in a just cause, a last resort, declared by a proper authority, possessing right intention, having a reasonable chance of success and with the end being proportional to the means used.