[TheDong]

No, that's what a write-ahead-log is, or quite a few various databases, or a git branch are.

The key innovation of the blockchain was the use of proof-of-work in order to associate an amount of computer-time with a given block, and then pick, from competing views of a blockchain, which view took the most energy to arrive at... all while being resistant to a small number of subversive actors.

In short, the blockchain solved the Byzantine Generals’ Problem, and happened to use a append-only cryptographic ledger as part of it.

[Jasper_]

Proof of Work doesn't determine which view took the most energy to arrive at. What it does is give a self-adjusting brute force cracking problem that takes 10 real-world minutes to perform, regardless of the amount of energy put in. The assumption is that 10 minutes is enough for even the slowest links of the network to get an up-to-view of the world, preventing double-spends or similar issues.

[dozzie]

> The key innovation of the blockchain was the use of proof-of-work in order to associate an amount of computer-time with a given block

Correct. In other words, proof of work is only a tool to make everybody slow in producing data while keeping everybody fast in verifying it.

> In short, the blockchain solved the Byzantine Generals’ Problem,

No. It's a common misconception, but in fact it does not solve Byzantine generals problem, with the simplest reason being that the problem requires the solving protocol to terminate (blockchain does no such thing).

> and happened to use a append-only cryptographic ledger as part of it.

The correct terminology is not "ledger", but "document timestamping". You don't need to record transactions in blockchain, they can be any statements. Cryptographers already had such systems, except that each of those required trusted third party to produce timestamps.