“IF it were necessary to give the briefest possible definition of imperialism, we should have to say that imperialism is the monopoly stage of capitalism.”
A special stage in the historical evolution of capitalism – the monopoly stage following that of (so-called) perfect competition investigated by Marx and Engels – this is how Lenin contextualises his specialised study in the general framework of Marxian critique of capitalism.
Monopoly refers, most obviously, to the giant corporations arising out of concentration of production –corporations which have become much more powerful today than in Lenin's time, not only in the economic arena but in the realms of politics and culture too. Thanks to the spate of mergers and acquisitions witnessed during the opening years of the present century, the degree of monopolisation has grown enormously. Just take a look at the business and non-business activities of, say, Rupert Murdoch's ever-expanding media empire and firms like Microsoft, Exxon Mobil, General Electric, Vodafone, etc, look at the way they almost dictate state policy, and you will see why present-day capitalism is best described as monopoly capitalism. In addition, Lenin referred to monopolistic control over sources of major raw materials like coal and petroleum; monopolies in banking and finance (the finance oligarchy) and so on. However, in all these areas, monopolies do not mean the end of competition. Monopoly grows out of, and further accentuates, competition between firms and nations, (trade wars among developed nations, for example) as we can see everyday everywhere.
In addition to monopolisation, Lenin drew attention to several other features of imperialism.