For Australia, the increased conflict between states, nations and various government entities will mostly be external (geographically) to the country, unlike the countries those wars will be fought in. Australia will not be a battlefield in the struggles between major or even minor powers, luckily due to geography (think of the distances and logistics involved). So for us, unlike Africa, parts of America and Asia etc. where the coming wars will be situated, increasing domestic instability is separate to foreign instability. In fact, most of the domestic instability common to collapsing civilisations isn’t likely to appear here since the rising spiral of external (e.g. invasions or raids) violence is a crucial part of the weakening of governments, peacekeeping forces (like police) and the breakdown of civil life that prevents many of the symptoms appearing. War bands can only function inside a country when either its military force is locked up stopping other problems or it’s ineffective/degraded. Rome had both of these problems, its defensive system was designed to stop large incursions but small warbands of 10-20,000 and raiding parties could penetrate every now and then while its military was being degraded by a shortage of funds, manpower and the stresses placed on it by a collapsing civilisation (such as a century of continuos civil wars and the regular stripping of the frontier forts this caused). Economics will cause the majority of the internal unrest and violence Australia will face, except in the North coast where Indonesia and New Guinea are close enough for external violence to manifest in forms ranging from piracy to invasion. However, the North coast’s population makes up such a small percentage, about 1%, that it won’t cause many problems.
Banditry and piracy are often a symptom of poor and broken economies and this is where most of the domestic strife will originate. As law enforcement is slowly restricted to the more urbanized areas and poverty increases those in the more rural areas will more often turn to thievery and banditry. This will push more trade towards the seas and along safer routes such as rail and further the process of making Australian society orientated around the coast. The increase of transport along the coast will make a tempting target for pirates, who will need sailing boats and safe harbours. The main hindrance for pirates off Australia’s south coast is that apart from the Bass Strait, is its all open waters and there isn’t a profusion of small islands for the pirates to use as bases. This will make many internal transport lines safe-ish for regular trade, the same however is not true for external lines, which are currently very important for Australia. A significant increase in the general crime isn’t actually that likely, without the breakdown of civil life even deep depressions don’t often see crime waves and a civil war that could shred civil life is unlikely even if the states separate. Wars of secession are much more likely, though a peaceful secession movement is more likely and while that could easily cause great disruption it is incredibly unlikely to destroy civil life to the degree necessary for major problems.
Dealing with large scale domestic strife would only take a few things; forming militias in small towns and villages to deal with local bandits with government support for some the guns, training and basic logistics. The rural police force will need to evolve to deal with the rise of rural banditry and reduced resources, expect horses to be used more often and some kind of travelling judge system developed. Civil and secession wars can be avoided by all parties agreeing to allow the decisions to be decided democratically, instead of what happened in South Vietnam where the South decided to pull out of the vote of wether to be communist or democratic and thereby cause the North to declare war. It’s easier in our case because we’ve been democratic since the beginning and our system works fairly well (South Vietnams didn’t and was fairly young), there aren’t any major ideological battles currently around and major interference by a foreign power is unlikely. Mostly maintaining democracy involves ignoring or delegitimizing the demagogues or the extremists who turn events violent and people extreme. Our National character isn’t one of fanatics or extremists, keeping it that way and marginalising the radicals who’s revolutions so often bring chaos is the main goal to stop this sort of momentous civil strife.
Dealing with the limited internal piracy has multiple solutions depending on the circumstances either an arming of merchant ships (big and small), an increase in the number of escort ships or simply denying the pirates friendly ports. The main danger of piracy is outside of Australia in the traditional pirate havens, and armed merchants are likely the best solution to that problem due to their distance from our shores. While the relatively small amount of piracy likely to be found on Australia’s coast can likely dealt with by either light single or double seater airplane patrols or police cutters. The main problem will be the lack of funding caused by economic crisis just as adaption is required.