As you already know by now, Bitcoin miners are the lifeblood of the Bitcoin ecosystem. They validate the transactions on the Bitcoin network, ensuring that double spending doesn’t take place. However, they do more than that, ensuring the security of the Bitcoin blockchain.
Blockchain networks are highly secure, but not all blockchains are as secure as the Bitcoin blockchain. Some blockchains are susceptible to 51% attacks, a type of attack in which a single entity controls the majority of the hash rate, causing a network disruption. The entity could modify the ordering of transactions and also possibly reverse transactions they’ve made preciously, leading to a double-spending problem. In 2018, over $20 million was lost in nine 51% attacks.
Bitcoin miners are the gatekeepers who keep this from happening in the Bitcoin blockchain.
Bitcoin miners are spread across the world. Unlike with smaller cryptocurrencies which can sometimes have the network hash rate concentrated within a few miners, Bitcoin’s universal appeal makes this close to impossible.
When Bitcoin was launched, it was made to be democratic in that the longest chain is perceived to be the legitimate one. Thus, if a malicious party got hold of enough computing power, he could secretly mine blocks on an alternate blockchain, running parallel to the legitimate one that the other nodes are mining. Once the chain belonging to the malicious party becomes longer than the legitimate chain the other nodes are mining, the other nodes are forced to accept the new chain as the legitimate one.
The only defense the Bitcoin blockchain has against such an attack are the miners. These miners ensure that in the spirit of self-interest, they verify transactions as fast as they can so that they can a bigger share of the block reward. In this competitive spirit, these miners ensure that no single malicious party has a stranglehold on the Bitcoin network.