in april 2017, samsung and exo collaborated on a special project for the samsung galaxy s8. on may 25, during a press conference at the olympic stadium of jamsil in seoul, the group announced their comeback in summer. baekhyun commented that the single from the new album was ready. on june 23, s.m. entertainment announced that lay would not participate in the comeback of the group due to his activities in china. exo's fourth studio album, "the war", was digitally released on july 18 and physically on july 19. the album contains nine songs including the lead single "ko ko bop". on september 21, s.m. entertainment announced that exo would return with the reissue of "the war" in early september. the title of the reissue was revealed as "the war: the power of music" and was released on september 5, 2017 with twelve songs including the new single "power".