War of the Worlds '15 was the second annual War of the Worlds event co-produced by ROH and NJPW, following War of the Worlds, which took place on May 17, 2014, at the Hammerstein Ballroom in New York City.

On January 4, 2015, at their Wrestle Kingdom 9 in Tokyo Dome show, New Japan Pro Wrestling (NJPW) announced that it would for the second year in a row co-produce an event with Ring of Honor (ROH) in May. At that point, no specific dates were announced and only the United States was named as a location. However, on February 25, ROH sent out a press release, announcing three co-produced events, as opposed to two shows in 2014, with War of the Worlds '15 taking place on May 13 in Philadelphia and Global Wars '15 on May 15 and 16 in Toronto, Canada. On March 7, War of the Worlds '15 was also expanded to a two-day event, taking place at the 2300 Arena over May 12 and 13. This was done due to the May 13 event quickly selling out. Both nights ended up being sold out in advance. ROH began announcing the NJPW wrestlers taking part in the events on April 1, starting with Hiroshi Tanahashi. Over the next nine days, ROH announced the remaining NJPW participants; Kazuchika Okada,Jushin Thunder Liger,Tetsuya Naito,Takaaki Watanabe,Kushida,Gedo, and finally Shinsuke Nakamura. On April 16, ROH announced that the Bullet Club trio of A.J. Styles, Matt Jackson and Nick Jackson would also be taking part in the War of the Worlds '15 events. The following day, ROH put additional standing room tickets on sale for the two events. On April 20, ROH announced all eight matches for the first night of War of the Worlds '15. All eight matches for the second night were announced the following day. Also announced were pre-show autograph sessions for May 12 and 13, which would be attended by both NJPW and ROH wrestlers taking part in the tour.

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