If the free and natural grouping of humanity is to both develop a structure for human unity and preserve the diversity of various cultures, peoples, etc. we should determine what institution of human societal organization has been developed by Nature to best suit this requirement. The family, clan, tribe, communal organisations are all too small and limited to undertake this role. The heterogeneous empire has had difficulty bridging the differences of peoples and cultures. The nation-state, however, appears to have the size and complexity needed to act as a foundational organization, to provide a basis for a psychological unity within, and a basis for interaction with other national units across the world.
Sri Aurobindo observes: “The natural unit in such a grouping is the nation, because that is the basis natural evolution has firmly created and seems indeed to have provided with a view to the greater unity.”
“…the free and natural nation-unit and perhaps the nation-group would be the just and living support of a sound and harmonious world-system. Race still counts and would enter in as an element, but only as a subordinate element. In certain groupings it would predominate and be decisive; in others it would be set at nought partly by a historic and national sentiment overriding differences of language and race, partly by economic and other relations created by local contact or geographical oneness. Cultural unity would count, but need not in all cases prevail; even the united force of race and culture might not be sufficiently strong to be decisive.”
Sri Aurobindo, The Ideal of Human Unity, Part Two, Chapter 18, The Ideal Solution — A Free Grouping of Mankind, pg. 162
Sri Aurobindo Studies 