"Useful Violence"

Came across this passage today in 'A Journey to the Western Isles of Scotland' by Samuel Johnson. "No faction of Scotland loved the name of Cromwell, or had any desire to continue his memory. Yet what the Romans did to other nations, was in a great degree done by Cromwell to the Scots; he civilized them by conquest, and introduced by useful violence the arts of peace. I was told at Aberdeen that the people learned from Cromwell's soldiers to make shoes and to plant kail. How they lived without kail, it is not easy to guess: They cultivate hardly any other plant for common tables, and when they had not kail they probably had nothing."