The idea that all humanity is one is a truth of existence that can be conceived by the higher reasoning powers of the mental consciousness. The divisions between different groups is an artificial construct born of the physical and vital existence which preceded the development of the mental awareness. The first awakening of the mental power relies heavily on the perceptions brought from the physical and vital life, and is very much influenced and controlled by the material and vital powers. Eventually, as the transition from the animal to the human life continues, and the higher reason begins to develop and take hold, it becomes possible to separate the ideas and perceptions which reveal themselves with the higher mind powers from those that are carryovers from the earlier stages of the evolution of consciousness.
The ideal of internationalism, the attempt to bring about human society as an expression of the inherent oneness of all humanity, is one such idea that begins to play in the minds of the evolved seers, thinkers, and philosophers who have shifted their awareness to a sufficient degree to perceive and express these higher ideals that appear to be contradicted by the outer life which remains fixed in its old habits. The weakness of internationalism, in the current day, is that it does not find its basis in the present life of humanity, but in some future that takes on a different shape and color than what most people can even imagine.
Sri Aurobindo notes: “The height and nobility of the idea is not to be questioned and certainly a mankind which set its life upon this basis would make a better, purer, more peaceful and enlightened race than anything we can hope to have at present. But as the human being is now made, the pure idea, though always a great power, is also afflicted by a great weakness. It has an eventual capacity, once born, of taking hold of the rest of the human being and forcing him in the end to acknowledge its truth and make some kind of attempt to embody it; that is its strength. But also because man at present lives more in the outward than in the inward, is governed principally by his vital existence, sensations, feelings and customary mentality rather than by his higher thought-mind and feels himself in these to be really alive, really to exist and be, while the world of ideas is to him something remote and abstract and, however powerful and interesting in its way, not a living thing, the pure idea seems, until it is embodied in life, something not quite real; in that abstractness and remoteness lies its weakness.”
Sri Aurobindo, The Ideal of Human Unity, Part Two, Chapter 32, Internationalism, pp. 279-280