From its beginnings in 1876 and throughout the first part of the 20th century, the Bell System grew from essentially local or regional telephone systems. These systems expanded by growing their subscriber bases, as well as increasing their service areas by implementing additional local exchanges that were interconnected with tie trunks. It was the responsibility of each local administration to design telephone numbering plans that accommodated the local requirements and growth. As a result, the Bell System as a whole developed into an unorganized system of many differing local numbering systems. The diversity impeded the efficient operation and interconnection of exchanges into a nationwide system for long-distance telephone communication. By the 1940s, the Bell System set out to unify the various numbering plans in existence to provide a unified, systematic approach to route telephone calls across the nation and provide efficient long-distance service that eventually did not require the involvement of switchboard operators.