But as capitalism exhausts the posibilities for primitive acumulation at the expense of pre-capitalist and intermediate social formations, so it has to look elsewhere for fresh sources of labour power. In the end, it has only one place to go. It has to canibalize itself. Some capitalists – chiefly via the credit system but also through patterns of tied sub-contracting to larger firms or dependency upon monopoly sources of supply. Others are forced into the proletariat directly, sometimes on a part-time and sometimes on a full-time basis, through heightened competition and bankruptcy. Other layers within the bourgeoisie likewise lose their former independence and become mere wage labourers albeit within a finely graded hierarchical system.

— David Harvey – Limits to capital (p. 437)