edit: see https://en.wikipedia.org/wiki/Warlord#Warlordism_as_the_domi...
> The other major consideration in categorizing warlords is through the lens of history. Warlordism was a widespread, dominant political framework that ordered many of the world's societies until the modern state became globally ubiquitous. Often warlord governance in pre-modern state history was constructed along tribal or kinship lines and was congruent with early perceptions of "nation." In colonial empires warlords served in both cooperative political capacities and as leaders of rebellions. In modern states the presence of warlords is often seen as an indicator of state weakness or failure. American historian David G. Herrmann noted, "Warlordism is the default condition of humanity."[5]
So, that's the highly "pure" form of libertarianism discussed in this thread (e.g., no government). A highly libertarian state is by definition very "weak" and we can observe that warlordism rises out of such states (as common sense would suggest in any case). Been there, done that.
Libertarianism in simple terms means emphasis on individualism and removing state from public welfare, education etc. These are the defining characterstics.
In all varitions of libertarianism except ancap, there is a government. It enforces a minimal constitution. Govt employs people such as police to enfoce it. Police are granted liberties that noone else have. Govt will be funded, most likely, with a flat amount "tax" per head.
> If the "police" here are hired as a private contractor, who is hiring them? the government ? (then you have government coercion).
Why its not coercion ? Because everyone explicitly consent to the constitution/govt. A democracy can only transition to libertarianism if 100% votes yes. Or secede.