Is blockchain the only technology for p2p decentralised global network? Are there any p2p decentralised cross border network structure out there?
One may also note that Blockchain is not a P2P technology per se, but rather just a  data-structure designed to reach global consensus provided with transactions acquired from a P2P network. Validation rules which govern the updates to this data-structure are consensus rules.

The actual Bitcoin P2P layer is similar to other P2P protocols(Gnutella, IPFS etc.), and is a messaging protocol designed to acquire and propagate public data with peers. Theoretically, a validating Bitcoin full-node may acquire its transaction/block updates from another channel/P2P protocol and still be in consensus.