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Justice Brennan, writing the leading judgement in Mabo No.2, observes that international law of the eighteenth century recognized that the:
'three main theoretical methods by which a State could extend its sovereignty to new territory were cession, conquest and settlement. Settlement was initially seen as applicable only to unoccupied territory. The annexation of territory by "settlement" came, however, to be recognized as applying to newly "discovered" territory which was inhabited by native people whom were not subject to the jurisdiction of another European State. The "discovery" of such territory was accepted as entitling a State to establish sovereignty over it by "settlement", notwithstanding that the territory was not unoccupied and that the process of "settlement" involved negotiations with and/or hostilities against the native inhabitants.'

In municipal law, 'sovereignty' means the right to govern a territory. The term harks back to the days when the monarch possessed supreme executive power. British sovereignty over Australia was effected when Captain Arthur Phillip read and published his second commission as Governor on 7 February 1788. Australia was deemed to be a 'settled colony'.

The Australian courts had made it very clear that they could not entertain argument regarding the legality of the act of State which established England's sovereignty over Australia. This argument is simply not justiciable in municipal courts. To support this proposition, Brennan J quotes from the judgement of the then Chief Justice Gibbs in the 1975 case of NSW v The Commonwealth:
'The acquisition of territory by a sovereign state for the first time is an act of state which cannot be challenged, controlled or interfered with by the courts of that state.' (1992) 175 CLR 1 at 31.

The plaintiffs did not dispute this line of authority and made no challenge to the validity of Britain's assertion of sovereignty over the new territory. Similarly, they made no challenge to the validity of the establishment of Queensland as a separate sovereign entity in 1859 nor to the validity of Queensland's annexation of the Murray Islands in 1879.
Keywords: annexation, Brennan, Justice Gerard, Mabo Case, Mabo v Queensland No.2, NSW v The Commonwealth, 1975, plaintiffs, sovereignty, sovereignty, terra nullius, 1992

(1992) 175 CLR 1, (1992) 175 CLR 1 at 31.
Author: Kenna, Jonathan
Source: Brennan, Justice