In this video from Finematics we learn about Vampire Attacks and how this plays a part in the SushiSwap saga.
It talks about the August 2020 launch of SushiSwap which started by forking (copying) the UniSwap process and siphoned out liquidity via a vampire attack. This essentially sees liquidity providers move from a platform they are on to another. This is done by giving incentives to move to the new platform (in this case 1000 new SushiSwap per Ethereum block).
That covers the first step. The second is to migrate staked LP tokens to the new platform as well and in doing this the new platform can use these pools of liquidity for their own AMM (Automated Market Maker). This means trading volume and users come over to the second platform.
The rest of the video goes through the short but storied history of SushiSwap. The jury is still out on what becomes of this and if it becomes a standard AMM in the DeFi space.