In Bitcoin and Ethereum, the longest chain with the most proof-of-work (POW) invested in it is accepted as the true chain and used to determine balances and history on the network.
Because of this, if an adversary wants to change a block in a blockchain of height at
h, he has to solve the POW for all blocks from
h up to the current block. This is very difficult.
However, with IOTA, the entire Tangle is not broadcast to the network similar to the way that blocks are mined and broadcast with Bitcoin.
What takes the place of nodes honoring the longest chain?
How does IOTA ensure that the consensus is permanent with an immutable Tangle?