This is the fifth in a series of posts marking the launch  of A Larger Australia, the book of the 2015 Boyer Lectures, by Lowy Institute Executive Director Michael Fullilove.

Australians have never really come to terms with the fact that we are the world's only continental nation. The vastness of our landscape, the distances between settlements, the smallness of our population and our isolation from the world's centres of power go some way towards explaining our lack of confidence on the world stage and our national habit of apologising for our good fortune. It may also explain the extraordinary pettiness with which we conduct our national politics.

While Malcolm Turnbull has brought a new tone of ambition, confidence and optimism to public policy, he still has among his followers the small-minded cynics who spent the last eight years talking down the economy and deriding those who wanted a more assertive Australia to play its role in the conduct of world affairs.

Both Tony Abbott and Julie Bishop, in opposition, mocked Kevin Rudd's efforts to secure Australia a seat on the UN Security Council as some kind of self-indulgent vainglory, yet were the principal beneficiaries of his success. Overseas travel by prime ministers, ministers and senior officials continues to be lampooned as boondoggling at a time when connectivity and representation are critical components of national prosperity.

The fact is that continued economic growth and long-term security depend on our ability to realise the potential that Australia's continental size affords us. This means that we need to be more engaged globally, and to do that we need to be bigger in every sense – bigger in mind, bigger in heart, bigger in aspiration, bigger in generosity and bigger in population. Strategically, size matters.

Stalin might have been right when he said that quantity has a quality all of its own, at least as far as rolling back the Wehrmacht was concerned. For Australia, however, quality and quantity are not polar opposites but facets of the same thing – size. And size is not a question of mass, but rather of weight, requiring us to think seriously about how we acquire it, how we sustain it and how we use it.

Australia's post-WW2 economic growth occurred on the back of a robust immigration policy and social policies that promoted the health and educational opportunities of the baby-boomers. While many look to the Snowy Mountains Scheme as the enduring symbol of an expansionary immigration program, the fact is that Australia's industrial development was probably the most enduring artifact of the flood of immigrants who brought with them skills and an appetite for hard work.

Yet there is a palpable reluctance among governments of all political hues to see a strong immigration program as a key driver of our national strength, wealth and resilience. The merging of the immigration and customs portfolios into a single entity – the Department of Immigration and Border Protection – with a concomitant shift of policy emphasis to border protection and a harsh refugee management policy, illustrates just how introspective and defensive we have become as a migrant nation.

To achieve Prime Minister Turnbull's aspirations for an innovative and thriving post-industrial economy, we need both to release the talent of young Australians through our tertiary education sector and to supplement that talent by encouraging young, educated people from around the world to make their homes here. With an enduring recession in Europe, a loss of confidence in the Americas and brakes on economic growth in Asia, the opportunity to bring in young professionals is unparalleled.

On current trends, the Australian Bureau of Statistics estimates a doubling of the population to 46 million by 2075. This is by no means a large population, especially considering the startling increases in longevity. Australia needs a progressive population policy that could plan for a population of say, 60 million, by 2075. A relatively small increase in net overseas migration would both mitigate the effects of a relatively low birthrate and reduce the average age.

There are, of course, many who point to the dryness of our continent and the size of our major cities as constraints on expanding our population. Yet advances in water recycling and water management, solar-powered desalination, improved agronomy and pasture management, along with enhanced urban design and the decentralisation of post-industrial employment would all serve to accommodate a larger and younger population.

Whatever strategic issues the 21st century generates, we can be sure that they will be multi-dimensional, multi-factorial, more multi-faceted and probably more intractable than anything we have experienced hitherto. A larger and stronger population would not only provide additional resources for national security – the result of a bigger economy – but would also provide the additional skilled personnel that will form the backbone of Australia's future defence industry and defence force.

Protecting and promoting Australia's strategic interests demand a continental perspective. While sound alliances are critical components of our national security policy, they only make sense to the extent that we maintain and sustain high levels of self-reliance that enable a serious contribution to both the durability and reliability of our strategic interdependence with allies.

To that end, size does matter.