Cross-chain history line

Single chain extension proposed (2012-2015)
Due to the limitations of block time, block capacity, and smart contracts, the development of Bitcoin has been severely restricted. Ripple Labs proposed the Interledger protocol as early as 2012 to solve the problem of collaboration between different blockchain ledgers. More innovations that followed, such as the emergence of Litecoin, Bitcoin shares, and Ethereum, accelerated the sense of crisis in the Bitcoin core development team. Therefore, in October 2014, the Bitcoin Core Development Group established Blockstream, and for the first time clearly proposed the concept of sidechain and protocol implementation in the white paper. In 2015, the Bitcoin Lightning Network adopted the Hashed Timelock mechanism to realize a fast transaction channel under the Bitcoin chain.

Relay and cross-chain platform (2016-)
In 2016, the BTCRelay program was published, which realized a one-way cross-chain connection from Bitcoin to Ethereum based on the relay cross-chain solution. In the same year, "Chain Interoperability" published by Vitalik Buterin made a comprehensive and in-depth analysis of blockchain interoperability issues.
In 2016, WanChain was born, which used multi-party calculation and threshold key sharing scheme to realize cross-chain transactions between public chains.
In 2017, Polkadot and Cosmos first proposed a plan to build a cross-chain basic platform, and these two projects are still in the development process.
In 2017, Ethereum Alliance and Polkadot founder: Gavin Wood formally proposed the concept of distributed-based Web3.0. web3 gave birth to monopolyism to the data equality movement, and blockchain is the vanguard of the data equality movement. The data equality movement allowed the concept of Web3.0 to emerge naturally. Web3.0 is not a technical category, but a decentralization to abstraction of a certain industry application trend.