Thinking on the Borg

Generally as things become more powerful they become more of a threat to others. The Borg though as they become more powerful will become less and less of a threat to other species, eventually they may reach a point in which they are not a threat to any species. The Borg's goal is perfection. In order to achieve perfection they assimilate other species technology and biology to add it to their own. If you are an inferior species they have no use for you and will leave you alone. Basically if you are not a threat to the Borg, and have nothing the Borg want, the Borg will ignore you. In Voyager it is stated that the Borg saw the Kazon as unworthy of assimilation and the were only interested in the Brunali when they saw technology they wanted. So civilizations that have nothing the Borg want either biologically or technologically are basically ignored by the Borg. What this means is as the Borg's technology advances and they get closer to perfection, more and more species will be ignored because they will have nothing to add to the Borg.