Based on my cursory understanding of the topic, The Merkle tree has been around for a while, but Satoshi figured out how to use that to achieve decentralization, and consensus building. If you ask me, that's quite revolutionary. Yes, the blockchain is just a gigantic DAG, but adding and deleting nodes on the graph is where the crux of the matter is I guess. I am starting to understand the logic from a currency perspective. Still trying to understand how the same translates to smart contracts.