The agreement to allow US Marines to be stationed in Darwin reflects a changing security dynamic in the Asia-Pacific region, in which the growth and strategic reach of China is the main factor. The United States seeks to construct a method of potential containment for any potential security challenge, with Australia being a lynch-pin in that policy. Under the US-Australia alliance, Darwin becomes a logical base at which to locate US Marine forces.
The question is, however, what this implies for Australian foreign policy and, to some extent, Australia's continued reliance on the US as its main guarantor in the international arena. Australia has been closely strategically tied to the US since 1942 and has committed itself to a range of pro-US military, strategic and diplomatic initiatives since then. Given that some of these initiatives have clearly reflected errors of judgment, such as the Vietnam War (the 'American War' to the Vietnamese), and the invasions of Iraq (ended without resolution) and Afghanistan (likely failure), there are grounds for questioning Australia's policy position.
However, while China does not present a direct or immediate threat to Australia, its strategic shadow is growing, now extending into the Indian Ocean (Sri Lanka), South-East Asia (Timor-Leste) and the Pacific (Fiji). These areas are of direct interest and potential concern to Australia. The US has already taken some 'soft power' measures to counteract China's growing influence, but the establishment of a 'hard power' option in Australia and in particular in Australia's northern reaches, makes strategic sense to both the US and to Australia as a longer term option. That the two countries have a strong history of alliance, despite its costs, mean that the establishment of a Marines base in Darwin is a logical next step.
Because of the costs - being tied to US strategic mistakes - many will oppose the establishment of the base in Darwin. But the costs of refusing such a base, in terms of Australia''s alliance with the US and its wider complex of strategic, diplomatic and economic linkages, mean that the only realistic option will concern the size, function and longevity of the base. The alternative is to break an association that would leave Australia internationally isolated which, as a self-proclaimed 'middle power', it does not wish to do, especially within its own rapidly evolving region.