The bitcoin whitepaper proposes a consesnsus model called proof-of-work which in the form of a key such that, when appended to the hash of a block of transactions and hashed, yields a digest starting with an agreed upon number of zeroes.

Attackers

Due to the hash of a previous block being an input into the hash of the current block, changes at any point in time in a transaction in a block will cause an inconsistency not just in that block but all blocks after it. Hence, an attacker trying to broadcast a faulty block of transactions onto the current consensus branch will need to continue to maintain the branch with the modified transaction.
However, the more the number of honest special nodes (called miners in relation to an analogy of gold-miners) that bear computing resources to determine the proof-of-work key, the smaller the chance for an attacker broadcasting a faulty chain of blocks to be the first to arrive at the proof-of-work.

Merkle Tree

Merkle Trees are binary trees that represent a list of items by storing hashes of the items in the leaf nodes and hashes of a node’s children in its inner-nodes
The Bitcoin whitepaper describes using Merkle Trees to save disk-space by discarding transactions in older blocks, without it affecting the hash of the block