Let's say I built a house on a land that belongs to no country. Now, whose house is it? It's mine as long as I can protect it. So property rights are defined not by some piece of paper, but rather by the ability to enforce them. Government is just one way to enforce property rights, I'd argue a rather inefficient one, since it usually can only deal with consequences of an intrusion (and not prevent it). In an absence of government, I could hire a private protection agency to enforce my property rights. And since many other people would be interested in doing the same, there will be a demand and prices would be very affordable.

So don't you dare say that I have my house because of the government.

So, say, the first American settlers used to own their houses because of an agreement with the British government - right? Now, at the exact moment they wished to secede, and started the War of Independence, they violated the agreement, and lost their property rights - right? So anyone could walk into anyone else's home, anyone could take anyone else's stuff... Communism! ;)

"Agreements" with sovereign powers are only sometimes worth the paper on which they're printed. A well-stocked armory, however, tends to retain its value in all climates.