Ethereum classic is, or was, built exactly the same as Ethereum used to be. There was a split in the community, similar to BCH, where there wasn't a unified agreement about how to act in response to the DAO exploit hack in 2016. An attacker made off with 3.6 million ETH, today that would be worth 11 billion dollars. The original dev team responded in rolling back the chain to a previous state, effectively rendering the attack null. Ethereum classic was forked and the response was that the decentralization of the chain shouldn't be affected by an attack.
Its sister chain has been attacked several times as there aren't as weren't as many miners keeping the chain safe. Attackers have been able to 51% attack the chain and allow double spending to take place and get all the block rewards. Despite this ETC remained true to its idea and didn't do any direct changes to the blockchain, instead they proposed and implemented changes to prevent the same attack from happening again.
Ethereum classic is a Proof-of-Work blockchain hard forked from Ethereum in 2016, bringing over any and all changes that Ethereum got before 2016. Computer running nodes are used to verify the transactions and creating new blocks. The process for doing so is very hard and requires a large amount of computing power, usually found in CPUs or GPUs. This expensive computing power exists as a hurdle that any attackers have to cross in order to perform an attack on the network.
The blockchain has avoided rolling back changes or attacks, staying true to a permissionless immutable blockchain. It does work and continuously implement new changes to help improve the chain. Two notable changes to the chain that sets it apart from Ethereum is that they have decreased the difficulty spike for subsequently created blocks & that there is a asymptotic supply cap, meaning that ETC will reach a max supply, same as Bitcoin. The blockchain is also interoperable with Ethereum, it receives updates to help integrate with Ethereum if there are changes made to its sister blockchain. This allows for easy transfer of Dapps onto ETC. There were also changes made to help increase the safety of the network following 51% attacks on-chain.
There are three distinct use cases for Ethereum Classic: payment, miner rewards & smart contracts. ETC is needed for performing any action on the blockchain. This is known as gas fees and is paid over to miners as reward for helping verify the blockchain. If there is a large number of smart contracts running on the platform that means that there is more transfer of ETC for gas fees, making it more lucrative for miners. This along with the smart contract also needing ETC to perform actions it increases the value of the crypto.
ETC has been in the shadow of its older sister, similar to Litecoin & Bitcoin. However it has segmented itself as a stable version of Ethereum that stays true to its original idea. With the incoming change to ETH 2.0 there are alot of miners that are scared if their investment into mining software will be rendered null. ETC will not move over to Proof-of-Stake and is a competitive alternative to mining Ethereum. It has managed to remain competitive and will need to keep making upgrades as there are a growing number of Proof-of-Stake blockchains that are power houses and offer immensely strong smart contract solutions. If Ethereum Classic can keep up or will be rendered obsolete, only time will tell.
