What Is the Role of the Blockchain’s Consensus Mechanism in Preventing Double-Spending?

The consensus mechanism, such as Proof-of-Work (PoW) in Bitcoin, ensures all network participants agree on the validity and order of transactions. Once a transaction is included in a block and that block is confirmed by subsequent blocks, it is virtually irreversible.

The longest chain rule dictates that the network accepts the history that required the most computational work, making it prohibitively expensive to reverse and double-spend.