Hearts of Iron IV is a Second World War grand strategy game developed by Paradox Development Studio and released in 2016, in which players control a nation through diplomacy, industry and warfare. Declaring war is one of its most consequential decisions, instantly changing alliances, fronts and production priorities, so the accompanying cue has become shorthand for escalation among strategy players. Shared through gameplay clips, edits and memes, it now signals that a joke, rivalry or fictional conflict has officially begun.