Let's talk about Ethereum's development history.
On July 20, 2016, Ethereum hard-forked at block 1920000 to address The DAO incident. The original chain, which did not follow the fork, continued as Ethereum Classic (ETC).
One thing worth thinking about: an Ethereum upgrade usually includes multiple EIPs. These are tested over several rounds on testnets, and the mainnet activation time is set only after stable operation has been verified.
Be cautious of claims like “you need to migrate your tokens for an upgrade”: Ethereum network upgrades do not require users to exchange their tokens.
$ETH has been Ethereum's native coin for paying gas since the mainnet launched in 2015.

This may not be entirely accurate, so use your own judgment.