This idea relates essentially that capitalist development does not occur in a homogeneous and even form, but rather, unevenness is the very essence of its development.
There are many different ways to look at this. Lenin made much out of the concept, but we can trace it back to Marx and his views about capitalist development and its relative virtues. Any reader of the communist manifesto will be perhaps shocked at the extent of Marx's praise of the revolutionary nature of the Bourgeoisie. For Marx, the particular character of the bourgeois mode of production lies in that it is compelled to reinvent the forces of production and correspondingly develop different political forms of relations between capital and workers, state and capital and state and workers. Hence the dynamic property of capitalism in its struggle with the working class (reduction of the cost of labour, whilst increasing labour power) leads to forms of development that continuously undermine older forms of social relations:
"The bourgeoisie cannot exist without constantly revolutionizing the instruments of production, and thereby the relations of production, and with them the whole relations of society. Conservation of the old modes of production in unaltered form, was, on the contrary, the first condition of existence for all earlier industrial classes. Constant revolutionizing of production, uninterrupted disturbance of all social conditions, everlasting uncertainty and agitation distinguish the bourgeois epoch from all earlier ones. All fixed, fast frozen relations, with their train of ancient and venerable prejudices and opinions, are swept away, all new-formed ones become antiquated before they can ossify. All that is solid melts into air, all that is holy is profaned, and man is at last compelled to face with sober senses his real condition of life and his relations with his kind." (Communist Manifesto)
This produces a tension in Marx's work between the power and revolutionary role of the development of the productive forces and the social effects of that process as they occur on the ground. In the preface to Capital for instance, Marx remarks upon the coexistence of older productive forms within the global market and the tremendous pressure that the general bourgeois relations bring upon these out-dated forms of production.
"We, like all the rest of continental Europe, suffer not only from the development of capitalist production, but also from the incompleteness of that development. Alongside of modern evils, a whole series of inherited evil oppress us, arising from the passive survival of antiquated modes of production, with their inevitable train of social and political anachronisms. We suffer not only from the living, but from the dead."
In comparison with earlier modes of production, capital relations are superior. It is not clear from what perspective, other than an unabashed confidence in the development of social productive power, the superiority of Bourgeois society is judged, for the political virtues that correspond to its development, equally and freedom are regarded as so much ideological cant, and the state is, as early as the Communist Manifesto, dismissed as the executive arm of the Bourgeoisie.
Another characteristic conflict of this type lies in Marx's writings about India in the New York Herald. Here British Colonialism is seen as a progressive force because it brings India to the level of development of a modern industrial nation. However at a later stage Marx was to emphasise the destructive side of colonialism. Arguably the tension here demonstrates the problem of uneven-development. In some places the imposition of the capitalist form of productive could be the very form in which productive developments are constrained or are prevented from taking their own course. India, today, of course remains under-developed in comparison to its colonial father, and paradoxically is upheld in this form as a virtue for the fledgling children of the western middle class.
It is perhaps the modern context of the productive ideology of sustainable development that maintains the relevance of the concept of uneven-development in this political sense today. The former Revolutionary Communist Party (U.K) in the shape of Living Marxism, now applauds the progressive nature of globalisation and celebrates the kind of sophistification of productive forces that Marx saw in British colonialism in India. Ignoring the inherent barbarism of the imposition of productive relations, the reconstitution of revolutionary subjectivity for this group lies in defending the Bourgeois project of development, now in ideological crisis and picking up the fallen gauntlet of modernist growth from the capitalist class. One could compare this point of view with that of Jurgen Habermas for whom the project of modernity has yet to be finished. But there is nothing more to this than really the desire to reaffirm the bourgeois model of subjectivity, of an instrumentally rational man. It is paradoxical that when the Bourgeois subject is in crisis, aspects of the left consider it their historical duty to reinvent this role, rather than going to the pub and having a good few beers in celebration.