Double spending is one of the most fundamental risks facing any digital currency. The ability to copy and reuse digital tokens threatens the security and trust of a monetary system.Before Bitcoin, this problem kept purely digital cash from becoming practical. Satoshi Nakamoto’s solution in 2009 changed that narrative, introducing a decentralized mechanism that made double spending virtually impossible.Key TakeawaysDouble spending is the main security risk that early digital money systems failed to solve.Bit ...