Private property goes pari passu with the state, more specifically with its laws. No state, no private property, because in the wild might is right: if someone stronger than you points at your property and says "that is mine" you can't do nothing but obey or be deprived coercively.
I could easily pay someone even stronger to protect my private property. Doesn't have to be state, does it?
Hypothetical:
1. I'm the guy stronger than you, and you ask me to protect your private property in exchange for some money.
2. I take your money, and, being stronger (and, as quickly becomes apparent, smarter) than you, also take the private property you paid me to protect.
3. ? ? ?
4. Profit!