Back when people with money could travel the roads, or the church was transporting idols, gold etc, way back when, the poor would resort to 'holding up' the coaches, horses, wagons etc. Famous theives include Robin (the) Hood (which is where the American term Hood or Hoodlum comes from) and Dick Turpin, who is probably the first 'Highwayman' saying the phrase "your money or your life". These are British references, hence the English phrase of your query, but I suspect the same was happening throughout Europe. Much later the tradition continued in the US, but I believe the term was a Mexican one: bandit(o) which suggests that it was the poorer Mexicans 'mugging/jacking' the richer colonialists. Generally the term "highway robbery" refers to a payment you have no choice but to make there and then (i.e. no bargaining, just a total handover of all that you have).