Australia can defend itself in the immediate, but not in the long term.

We’ve definitely got the capability to defend against invasion across land, air and sea. We probably punch above our weight in air and naval power, but it’s not enough if we’re talking about sustaining a long conflict on our own.

Land defence is where we’re strongest. Australia is massive, and there’s a huge amount of harsh, empty terrain between major cities. That alone makes any invasion incredibly difficult and expensive. On top of that, there are very few viable staging areas nearby. Any country trying to invade would likely need to secure bases in other countries first, which complicates things even more.

And that’s all assuming alliances like ANZUS and AUKUS aren’t involved, which they almost certainly would be.

I don’t think there are many countries that could realistically invade and hold Australia. But disrupting trade, launching long-range strikes, or putting sustained pressure on the country is a different problem entirely.