Real estate is property consisting of land and the buildings on it, along with its natural resources such as growing crops (eg. timber), minerals or water, and wild animals; immovable property of this nature; an interest vested in this (also) an item of real property, (more generally) buildings or housing in general. In terms of law, real is in relation to land property and is different from personal property while estate means the "interest" a person has in that land property. Real estate is different from personal property, which is not permanently attached to the land (or comes with the land), such as vehicles, boats, jewelry, furniture, tools, and the rolling stock of a farm and farm animals. In the United States, the transfer, owning, or acquisition of real estate can be through business corporations, individuals, nonprofit corporations, fiduciaries, or any legal entity as seen within the law of each U.S. state. The natural right of a person to own property as a concept can be seen as having roots in Roman law as well as Greek philosophy. The profession of appraisal can be seen as beginning in England during the 1500s as agricultural needs required land clearing and land preparation. Textbooks on the subject of surveying began to be written and the term "surveying" was used in England, while the term "appraising" was more used in North America. Natural law which can be seen as "universal law" was discussed among writers of the 15th and 16th century as it pertained to "property theory" and the inter-state relations dealing with foreign investments and the protection of citizens private property abroad. Natural law can be seen as having an influence in Emerich de Vattel's 1758 "Law of Nations" which conceptualized the idea of private property. One of the largest initial real estate deals in history known as the "Louisiana Purchase" happened in 1803 when the Louisiana Purchase Treaty was signed. This treaty paved the way for western expansion and made the U.S.