A full on invasion of Australia may seem absurd and near impossible, however we cannot count on the fact that Australia will go without a military threat forever. Australia has a plethora of important resources that are extremely valuable to other countries. In fact, our supply of coal can generate enough power required for another 300 years. Additionally, Australia has a rich economy that has great potential. Our huge land size would be valuable to conquer and colonize as it has less than half the population of other countries of the same proportion. However, chances are slim that a superpower, or any other country for that matter, will perform a full on invasion of Australia. A country that has the ability to carry
out an invasion to that extent like China would have done so long ago, and not just to Australia, but to other less powerful countries if they wanted. Other countries are even more unlikely to do so as they know it is not an easy or ideal task. Firstly, developing enough ammunition and sustaining large forces across the sea would be difficult to go unnoticed; Australia would have time to react and prepare. Secondly, significant amounts of resources would be needed to do a full out invasion of Australia; the costs would be extremely high and most likely not worth it. Lastly, controlling and conquering Australia is very unlikely as the mainland is massive and the population is dispersed all around the country. In any case, an invasion of Australia cannot be ruled out completely, but it isn't to be expected either.