How did the land of John Knox's become so Left-wing?

How did the land(Scotland) of John Knox become so Left-wing? Of course,tomorrow Scotland votes weather or not to leave the U.K. It's interesting the Tories only one seat in Scotland out around 70 seats.Labor will lose big if Scotland goes it's own.But how did Scotland become Socialist?Presbyterian Scotland is last place you think Karl Marx would made an inprint,but it happen.