It is without justification that money has been called one of the greatest inventions of mankind.
The English is weird here, but if I’m reading the Japanese right, I would expect it to be “It is not without justification that…”, i.e. “There’s a good reason that…”
@kebukebu
Your understanding is correct 
The Japanese sentence means “There are some solid reasons/evidences why currency has been called one of the greatest inventions of mankind.”
十分な as in 十分な理由 here can be referred to either the quality (i.e. bulletproof evidences) or the quantity (e.g. the same conclusion deducted from multiple sources).
I don’t know why the English sentence says “it is without justification”… Maybe the English author misinterpreted the phrase 十分な理由 as 言い訳 (excuse to justify one’s behavior). Or “justification” might be just a typo.