In anglophone academic works, theories regarding imperialism are often based on the British experience. The term "Imperialism" was originally introduced into English in its present sense in the late 1870s by opponents of the allegedly aggressive and ostentatious imperial policies of British prime Minister Benjamin Disraeli. It was shortly appropriated by supporters of "imperialism" such as Joseph Chamberlain. For some, imperialism designated a policy of idealism and philanthropy; others alleged that it was characterized by political self-interest, and a growing number associated it with capitalist greed. Liberal John A. Hobson and Marxist Vladimir Lenin added a more theoretical macroeconomic connotation to the term. Lenin in particular exerted substantial influence over later Marxist conceptions of imperialism with his work Imperialism, the Highest Stage of Capitalism. In his writings Lenin portrayed Imperialism as a natural extension of capitalism that arose from need for capitalist economies to constantly expand investment, material resources and manpower in such a way that necessitated colonial expansion. This conception of imperialism as a structural feature of capitalism is echoed by later Marxist theoreticians. Many theoreticians on the left have followed in emphasizing the structural or systemic character of "imperialism". Such writers have expanded the time period associated with the term so that it now designates neither a policy, nor a short space of decades in the late 19th century, but a world system extending over a period of centuries, often going back to Christopher Columbus and, in some accounts, to the Crusades. As the application of the term has expanded, its meaning has shifted along five distinct but often parallel axes: the moral, the economic, the systemic, the cultural, and the temporal. Those changes reflect - among other shifts in sensibility - a growing unease, even squeamishness, with the fact of power, specifically, Western power.