Actually the concept that the state could appropriate ones lands has been around for many centuries.
The US Constitution has in it the following clause 'nor shall private property be taken for public use without just compensation' to limit the ability of the government, often in Britain the king, the right to take away anyone's property, for whatever reason, including whim.
That clause is in the Fifth amendment, tacked onto the end of the sentence that gives villians, thieves, and even DCer's the right not to self incriminate.
The use of eminent domain has until recently been limited to use by the gov'ment for roads, airports, bridges, that sort of thing.
In the last few years private companies have used the courts to allow the usurpation of private property for 'the better good'. In other words a developer might be able to request the law allow the taking of people's properties considred undesirable by many to build a tony development, for the better good.
This was at least partially halted by GWB (not a political statement). How this whole thing will play out remains to be seen.
But the simple answer to the question is that you may think you own the place that is your castle, but others may be able to take it away whether you wish to sell or not.
