In 2000 Roy Fielding publishes his doctoral thesis at UC Irvine, defining REST as a set of architectural principles for distributed web systems: uniform interface, statelessness, cacheability, layered system, optional code-on-demand, and client-server architecture. REST leverages existing HTTP infrastructure, drastically reducing implementation complexity compared to SOAP/RPC, and progressively displaces SOAP as the dominant style for web APIs throughout the 2000s.