They're not Australian when their founders are Scottish. Formed in Australia, yes ... but the main founders are Scottish.
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That is true, just giving my home nation the "attention" it deserves. To ignore the Scottish roots of AC/DC and solely call them Australian is a tad unfair. The brothers are highly thought of back home in Glasgow's rock circles.
Would Van Halen be considered an American Band or a Dutch Band? The Van Halen brothers are from the Netherlands but the band was formed in California.