Every function in the child's cultural development appears twice: first, on the social level, and later, on the individual level; first, between people (interpsychological) and then inside the child (intrapsychological). This applies equally to voluntary attention, to logical memory, and to the formation of concepts. All the higher functions originate as actual relationships between individuals.
Four years of world war, at a cost in human suffering which our minds are mercifully too limited to imagine, led to the very clear realization that international anarchy must be abandoned if civilization was to survive.