Hearts of Iron IV, developed by Paradox Interactive and released in 2016, is a grand strategy game set during World War II in which nations can join factions such as the Allies, Axis, or Comintern. The join faction notification is one of its many interface sounds, designed to alert players to a diplomatic change without interrupting gameplay. As HOI4 gameplay, memes, and strategy guides spread on YouTube and TikTok, editors began lifting the short chime to signal alliances in their own edits, and it has stayed popular because it is instantly recognisable to strategy fans.