Revolutionary thinking taking sheep onto busy road heading north? (7)
I believe the answer is:
marxism
'revolutionary thinking' is the definition.
'sheep onto busy road heading north?' is the wordplay.
'sheep' becomes 'ram' (ram is a kind of sheep).
'onto' means one lot of letters go next to another.
'busy road' becomes 'msix' (the M6 is a motorway).
'heading north?' says the letters should be written backwards.
'ram' after 'msix' is 'msixram'.
'msixram' written backwards gives 'MARXISM'.
'taking' is the link.
(Other definitions for marxism that I've seen before include "Left-wing philosophy" , "Left-wing ideology" , "Political doctrine" , "Left-wing system" , "Communist belief" .)