Is the Creation of States (Polities) Justified? By What Means?

[Final-Fan]

[edit:  Oops, didn't notice the age of the previous post.] 

Mightn't the "promises aren't enforceable" idea come into problems with goods-for-services arrangements? If I say I'll mow your lawn for $20 and you give it to me before I mow, oops I don't want to, thanks for the dough. You say you'll pay me after, but then say "I hope you liked the exercise". Sure, a person who did this all the time would end up with a bad reputation, but that is a less effective deterrent in a large, mobile society.

Another thing: in your initial example, you say Rothbard would hold that the person has the right to accept the dog in trade, but then (when the other person demands the chicken) decide he doesn't want it, and return the dog, having canceled the "promise", without repercussion. What if the dog died in the meantime? If it was just a promise that was canceled, then wouldn't it just revert ownership, giving the guy back a dead dog? If not, does the guy with the chicken have to hand it over? Why?

I guess one problem I have is the question of when the ownership of property actually transfers. If it hasn't transferred by the time one party has accepted the other party's payment, then why does it EVER fully transfer? Does it ever?  Could I unilaterally "undo" a transaction that occurred an indefinite length of time in the past?