“Minarchism is defined as a libertarian philosophy”
And those who do so would be wrong ;-)
This source seems to be pretty authoritative:
https://www.econlib.org/archives/2015/06/the_incredible_3.html
Jun 17, 2015 - In the 70s and 80s, a great intellectual battle waged between two libertarian factions: minarchists and anarcho-capitalists.