Replying to myself since we hit max comment depth (probably an indicator it's time to move away from this thread anyway). but to address the sibling reply by hudon, yes, a blockchain is a form of a distributed database (maybe highly replicated data base is a better term since every node has the full working data set).
The key trait of a blockchain is that each new entry cryptographically verifies all previous entries. At the end of the day, yes, a blockchain is a distributed db. It's a distributed db that never forgets.
> The key trait of a blockchain is that each new entry cryptographically verifies all previous entries
I see what you're saying. Basically: distributed database + signatures + merkle tree = blockchain.
I usually use this definition: decentralized and sybil-resistant database + signatures + merkle tree = blockchain.
So I think the key trait that turns a distributed database into a blockchain is not the merkle tree, but is its decentralized nature. Anyone can be a transaction validator and no one can prevent transaction validation.
The key trait of a blockchain is that each new entry cryptographically verifies all previous entries. At the end of the day, yes, a blockchain is a distributed db. It's a distributed db that never forgets.