What Is the Main Defense Mechanism against a 51% Attack in Proof-of-Work Systems?

The main defense mechanism against a 51% attack is the immense economic cost required to acquire and maintain the necessary hashrate. The high capital expenditure and operational costs (electricity, hardware) act as a deterrent.

Additionally, the decentralized nature of mining pools and the community's ability to coordinate a hard fork to change the mining algorithm can mitigate the attack's long-term success.

How Do Hashrate Rental Markets Impact the Economic Security Model of Proof-of-Work (PoW) Coins?
How Do Reputation Systems Work in Conjunction with Crypto-Economic Incentives?
What Is the Primary Defense Mechanism against a 51% Attack on a PoW Network?
Does the Type of Mining Algorithm (E.g. SHA-256 Vs Scrypt) Affect the Cost of a 51 Percent Attack?
How Does the Cost of Acquiring 51% of Hash Power Impact the Feasibility of an Attack?
How Does Decentralization of Hashrate Distribution Contribute to Network Security?
Why Is Proof of Work Considered Secure?
What Defense Mechanisms Can Be Deployed against a Sybil Attack on an Oracle Network?

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