Re: only if they lost ...
Just War theory is a doctrine of military ethics of Roman philosophical and Catholic origin studied by moral theologians, ethicists and international policy makers which holds that a conflict can and ought to meet the criteria of philosophical, religious or political justice, provided it follows certain conditions.
The Just War Theory was asserted as an authoritative Catholic Church teaching by the United States Catholic Bishops in their pastoral letter, The Challenge of Peace: God's Promise and Our Response, issued in 1983. More recently, the Catechism of the Catholic Church, in paragraph 2309, lists four strict conditions for "legitimate defense by military force":
the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain; all other means of putting an end to it must have been shown to be impractical or ineffective; there must be serious prospects of success; the use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modern means of destruction weighs very heavily in evaluating this condition.