The landmark shift in US national security policy to prioritise the threat posed by powers like China and Russia could prompt a rethink of Australia's defence spending, according to an incoming senator.

Key points: The US National Defence Strategy states China and Russia are "undermining" international order

The US National Defence Strategy states China and Russia are "undermining" international order Retired Major General Jim Molan says the US has been carrying a disproportionate burden in defence spending

Retired Major General Jim Molan says the US has been carrying a disproportionate burden in defence spending He thinks America will expect more from Australia

American Defence Secretary James Mattis has outlined the country's strategic military objectives, and said terrorism was no longer the most serious threat the nation faced.

He said that concern was now outpaced by the rapid rise of China and Russia's increasing aggression.

Retired Major General Jim Molan is an incoming Liberal senator and said he believed the statement from Australia's closest defence ally had important implications for Australia.

"The output of defence is winning the next war," he said.

"You can see what the next war is likely to be if you look at the national security strategy and the national defence strategy of the US and prepare for a role we might have in that."

While the new Liberal recruit was not prepared to offer advice about whether the defence budget should be bolstered, he hinted at that outcome.

"America has been carrying a quite disproportionate burden of the kind of defence spending that creates the stability that makes us all prosperous," he said.

"Now the Americans will be expecting more of us."

It is not the first time the senator-elect has talked about Australia's defence spending — earlier this month he warned America's armed forces were depleted and would not be able to guarantee Australian security if domestic fuel reserves ran dry.

Australia is aiming to increase spending on defence to 2 per cent of GDP by the end of decade.

"If 2 per cent of GDP was the aim when America dominated the world … then there is probably a different amount now that America has reduced its own defence spending and defence capability and those that challenge it have increased theirs," the incoming senator said.

"We're seeing invitations, particularly in the Prime Minister's visit to Japan of a great realignment of allies within the region."

Defence Minister Marise Payne said in a statement that "like the United States, Australia is prepared to pay for its security, as well as play its part in strengthening its longstanding alliance with the US".

"The Government remains on track to lift defence spending to 2 per cent of GDP by 2021."

A summary of the US National Defence Strategy document noted the "network of alliances and partnerships remain the backbone of global security".

The document also stated "China and Russia are now undermining the international order from within".

"The Australian Government welcomes the release of the Trump Administration's National Defense Strategy," Senator Payne said in the statement.