There was a lot of talk about history when Prime Minister Lee Hsien Loong came to Canberra earlier this month. Both he and his host, Australian PM Malcolm Turnbull, framed their glowing accounts of today's vibrant Singapore-Australia relationship by speaking of our shared past.

They mentioned Australian troops' involvement in protecting Singapore from its fall to the Japanese in 1942, the struggle against communist insurgencies in the 1950s, and the resistance to then Indonesian President Sukarno's Confrontation against Singapore and Malaysia in the 1960s. These were all trials that Australians and Singaporeans faced together, and our leaders were right to emphasise these shared experiences as a foundation for the remarkable links we have built since those turbulent times.

But history can only take us so far.

Politics and statecraft are about shaping the future, and the big question that our leaders face today is how Australia and Singapore might cooperate to face the challenges ahead. So we have to do more than simply celebrate our shared history; we have to think carefully about how its lessons can be applied to build the relationship we will need over the decades to come.

Those decades seem likely to pose challenges for both countries, and for the whole region, that are different from those we have known in the past. Both leaders referred to these challenges in their formal speeches during PM Lee's Canberra visit, especially the challenges to building and sustaining a stable regional order among Asia's jostling great powers at a time when relations between them are shifting fast.

Both expressed confidence that Australia and Singapore would and should continue to work together because they will continue to share a close alignment of interests. That will be important, because the signs are many that the issues we face over the coming years will not just be different from those we have known in recent decades, but also more complex and potentially more dangerous.

So it is worth looking beyond our leaders' warm words and ask why we should be confident that this relationship will not just remain of major importance, but quite probably become of growing importance, to both countries.

CONVERGING INTERESTS

To do that, we need to recognise that what matters is not the historical record itself, but what that record shows about each country's enduring strategic interests and how they converge.

Here in Australia, we have given a good deal of thought to such things. In our defence and strategic policy planning, we define strategic interests as those features of our international environment that, over the long term, most influence the probability that we might face a serious military threat.

Over the past 20 years, successive defence policy documents and White Papers have spelled out quite explicitly what Canberra believes those features are, drawing on ideas which have guided Australian defence and diplomacy for generations.

A glance at the map will tell you that Australia's most important strategic interests are concentrated in the huge archipelago north of Australia that stretches from Sumatra all the way to the islands of the South-west Pacific.

This vast swathe of islands can serve either as a barrier to any hostile power trying to approach our remote continent, or as a highway for it.

LESSONS FROM HISTORY

In the words of one of Australia's most influential strategic thinkers, geography determines that any serious attack on us must come "from or through" the archipelago. And history tells us that such threats can emerge in either of these two ways.

The indelible lesson taught by the events of 1942 is that the intrusion of a potentially hostile major power into the islands of maritime South-east Asia increases Australia's strategic risks enormously. And conversely, the best way to keep Australia secure is to ensure that no potentially hostile major power succeeds in gaining a major foothold in the South-east Asian archipelago.

This was why Australia was content to entrust its security in the 1930s to the British commitment to hold Singapore, why we committed so many of our forces to Singapore's defence, and why the fall of Singapore was such a disaster for us, as well as for Singapore itself.

That lesson was applied again in the 1950s and 1960s, when Australia feared that attempts by communist China to gain political influence and strategic presence in South-east Asia posed a new threat to our interest in preventing major power intrusion into maritime South-east Asia.

That was why it was so important to Australia that communist subversion should be successfully resisted. And that was why Australia, through its Forward Defence policy of those years, was so committed to helping that resistance with long-term force deployments and active combat operations, especially in the Malayan Emergency and later, of course, in Vietnam.

We also learnt in the 1960s that threats could emerge from within the archipelago when, under Mr Sukarno, Indonesia began to pursue aggressive policies towards its neighbours.

Australia recognised that its security depended not just on preventing the intrusion of major powers into our nearer region, but also on preventing the emergence of an assertive and disruptive close neighbour. And that why it was so important to Australia that Confrontation be successfully resisted, and why Australia was committed so strongly to supporting Malaysia and Singapore to do that.

Fortunately, of course, both these kinds of threats evaporated in the late 1960s and early 1970s. Indonesia, under Mr Suharto, became and has ever since remained a most constructive, valued and responsible neighbour and regional partner, and China has emerged as a major force for regional growth and integration. We have enjoyed a long era of remarkable stability and peace ever since.

But Australia has not forgotten those lessons of history and what they teach us about the enduring strategic interests on which our security depends. Nor have we forgotten how valuable Singapore can be to Australia as a partner in protecting those interests. And we believe this history suggests, too, that Singapore's long-term strategic interests are very likely to remain similar with Australia's.

That is why, through the decades of peace since the early 1970s, Australia has always so highly valued its strategic relationship with Singapore. That is why we have remained committed to the Five Power Defence Arrangements, and take so seriously the obligations we have accepted under those arrangements to go to Singapore's aid if it is attacked.

And that is why Australia so warmly welcomes the growing cooperation between our armed forces, reflected especially in the ever-expanding training opportunities that the Singapore Armed Forces enjoys on Australian soil.

Prudent statesmen do not, of course, talk too explicitly about such things - at least in public. But it is important to know that behind the warm words our leaders exchanged in Canberra, there lies a very solid basis in history and geography for close cooperation in the uncertain years and decades ahead.

•The writer is professor of strategic studies at the Australian National University in Canberra.