According to the orthodox principles of private international law, as applied within Australia during the twentieth century, the different States are essentially to be regarded as foreign entities. At common law, the courts of one State will generally apply the statutory laws of another State to resolve a civil law dispute if directed to do so by the common law choice of law rules, but not otherwise. Yet federation was a eustatic event in the evolution of the Australian legal system, albeit that the sea change has taken some time to flow through to many areas.
Australian States are not foreign nations but sub-entities within one nation established and maintained by the Australian Constitution. The law to be applied when there is some competition between Australian legal rules cannot appropriately be dictated just by the common law. That raises constitutional questions by its very nature.