Arrowverse
The CW began airing Arrow in fall 2012. The program was very successful. This caused the network to make a The Flash spin-off the next year. Barry Allen was planned to be in the eighth and ninth episodes of the second season of the series. The twentieth episode of that season was to be used as a backdoor pilot for the new series. After the people in charge saw the first episodes, they decided to order a pilot episode for the series rather than waiting until the end of the season. In early 2015, the CW announced a web-series for Vixen to air on the CW Seed. Two months later, The CW said an additional series, DC's Legends of Tomorrow was to be be broadcast in early 2016. On August 12, 2015, Wendy Mericle said their version of John Constantine would follows the same continuity as NBC's Constantine. On December 12, 2018, Marc Guggenheim said their version of Barry Allen follows the same continuity as CBS's The Flash.