The Nabataeans were an Arabian tribe that, in the age of the Persian Empire, settled in the kingdom of Edom. The Greeks were unable to conquer them, although they tried in c.312 BCE, and the Nabataeans retained their independence, outside the Hellenistic world. Later, when the Roman commander Pompey the Great reorganized the Near East, they again managed to retain their autonomy.
The key to their independence was, at least partly, their control of the Incense Route: a caravan route through the western part of what is now Saudi Arabia, all the way to Yemen, where spices and incense could be found. As long as they controlled trade, they were left alone. However, once Rome had conquered Egypt, trade was increasingly often conducted by sailors, and Nabataean income diminished. In 106 CE, the Roman emperor Trajan annexed the country of the Nabataeans.
My new page on this subject is here.