Not even the Catholic Church agrees with you and they're famously aggressively anti-war. From Pope Francis, “war is in itself a crime against humanity.” John Paul II, "No, never again war, which destroys the lives of innocent people, teaches how to kill, throws into upheaval even the lives of those who do the killing and leaves behind a trail of resentment and hatred." And yet church doctrine outlines the criteria for a just war.

1. The damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain.

2. All other means of putting an end to it must have been shown to be impractical or ineffective.

3. There must be serious prospects of success.

4. The use of arms must not produce evils and disorders graver than the evil to be eliminated.

The US gets tripped up on 4. a lot.

So the Ukrainians should not be defending themselves against a foreign invasion?

Defending themselves against foreign aggressors who have committed documented atrocities against their population, and who are on record as intending to commit genocide against them when they win, is immoral?

Resisting occupation?

Wars and conflicts have been around long before we had defined morals.