Given that all courties had slaves at ons point or another, so it would be the sin of the WORLD not just the USA.
In short, no, there is no nation that has never had slavery. In almost every civilization, captured prisoners from battles or raids were almost always forced to work as laborers or servants within the enemy society and had very few rights or liberties. There is no recorded case of any region in the world that has not had slaves, as it is an almost universal trait in most early civilizations.
Australia never had "official" slaves - people were never bought and sold per se. A convict's indenture could be bought, but always on the understanding that when the sentence was completed, the emancipated man/woman was free. Lifelong slavery didn't happen.
Was the person allowed to leave? Then they were a slave. And if they were paid/indentured servants, why does the gov offer money to descendants? And might want to look up the history of blackbirding in Australia. Australia is not clean when it comes to slavery.
The practice was illegal - but due to the impotence of the colonial government in Queensland, the law was not enforced. It was stamped out as soon as Australia gained independence in 1901. Official slavery was never countenanced. Indentured labour isn't quite the same thing and you know it. A convict had freedom as soon as their sentence was complete - so in effect it was the "hard labour" part of their imposed sentence being performed outside of a prison setting.
The article says they are offered money from the gov for a "lifetime of forced labor" There was slavery....it was wrong and we all stopped. And it was not all indentured servants. The people were bought and forced to work for free in the pearl industry and the sugar industry.
You can hide behind the independence date all you want but the region and the people in it had slavery.....real slavery. Not just debtors.