Possibly as a response to outer crises faced and overcome together, smaller units of society have successfully formed and developed larger units, and even developed psychological unity. This does not occur in every case, particularly where disparate peoples and cultures have been fused together by outward, mechanical means, and especially when those means have included warfare, domination and oppression to achieve their ends. It was just such a process that led to the fusion of 13 colonies in the United States of America, despite some differences in economic system, religious denomination and issues such as slavery. Banding together to overthrow the British rulers showed these people the benefits of working together for a common goal. Tensions over the internal differences were suppressed until they broke out during the Civil War. In the interim, the economic and political unity bonded into a nation-unit with a great deal of psychological unity, although present day stresses make it seem like the psychological unity has not yet stabilized.
Sri Aurobindo observes: “But, secondly, there is the force of a common uniting sentiment. This may work in two ways; it may come before as an originating or contributory cause or it may come afterwards as a cementing result. In the first case, the sentiment of a larger unity springs up among units which were previously divided and leads them to seek after a form of union which may then be brought about principally by the force of the sentiment and its idea or by that secondarily as an aid to other and more outward events and causes.”
“The larger national aggregates have grown up by a simple act of federation or union, though this has sometimes had to be preceded by a common struggle for liberty or a union in war against a common enemy; so have grown into one the United States, Italy, Germany, and more peacefully the Australian and South African federations. But in other cases, especially in the earlier national aggregations, the sentiment of unity has grown up largely or entirely as the result of the formal, outward or mechanical union. But whether to form or to preserve the growth of the sentiment, the psychological factor is indispensable; without it there can be no secure and lasting union. Its absence, the failure to create such a sentiment or to make it sufficiently living, natural, forcible has been the cause of the precariousness of such aggregates as Austro-Hungary and of the ephemeral character of the empires of the past, even as it is likely to bring about, unless circumstances change, the collapse or disintegration of the great present-day empires.”
Sri Aurobindo, The Ideal of Human Unity, Part Two, Chapter 35, Summary and Conclusion, pp. 302-303