As this line erodes, the principle of non-intervention must also weaken.
Four weeks later, the Labour leaders declared that the Spanish government should have the right to buy arms and in 1937 both the Labour Party and the TUC condemned the policy of non-intervention .
Moreover, collective security had been developed within the framework of a clearly defined inter-state order enshrining principles of sovereignty and non-intervention .
This competitive logic of power politics makes agreement on universal principles difficult, apart from the principle of non-intervention in the internal affairs of other sovereign states.
The ideological dispute between absolutists proclaiming a right of intervention to suppress revolutions and liberals proclaiming a doctrine of non-intervention made little difference in practice.
It is one of the masks worn by English surrealist artists in a protest against the British government policy of non-intervention .
The crucial choice - of non-intervention , sanctions, or war - will ultimately be dictated by national interests alone.
So does humanitarian intervention violate the UN Charter's acceptance of the principle of non-intervention in the domestic affairs of another sovereign state?
One certain consequence was that Britain and Russia agreed on a future policy of non-intervention , thus making it possible for China to reassert its authority.
This is not an easy conundrum to resolve and each tactic - intervention and non-intervention - carries risks.