And why do they have to have the intent on extracting the resources? Since when is that a test for property rights?
Regarding our government defending property rights abroad, I agree that an American citizen (or a corporate citizen) should not expect our government to protect his rights abroad with the same energy as at home. The typical role of our government is to defer to the laws of the foreign land. However, when such laws are at significant variance with the natural law, or simply are not enforced, then our government may have a cause for war.
The only cause for war should be to repel an act of aggression which threatens our Sovereignty. Nothing more, nothing less. Oil is no excuse.
Nor is being "technologically backward." While you inist you don't want to use the word "savages" you use an interchangable term and pretend that you aren't thinking within that box. Soveriegnty, if respected, allows countries to make their own decisions including being technologically backwards. The principles of freedom demand that we respect those decisions.
Just cause of violence is to prevent an imminent threat of violence or retaliate for an act of violence committed against an individual. Abstract violations of sovereignty have nothing to do with just causes of war; concrete harm to citizens does.
The technological development is relevant to the extent that it allows us to grant the oil in the desert rights to Exxon, which has the technology.