It's difficult to know because the written records dwindle as time progresses backward and there's no method of measuring ruthlessness. Of those with records the Israelites were certainly as ruthless as most, far more so than the Romans during most of their watch [assuming their accounts in the Bible are accurate.] Mongols were conspicuously ruthless by most accounts, but a lot of them might be biased. And some of the ancient Chinese dynasties were. The Christians spent most of 2000 years being as ruthless as human beings can get and still call themselves human.
