Thought it refers to the beginning of the American War for Independence:
https:// www.nps.gov/mima/learn/education/the-shot-heard-round-the-world.htm
>The "shot heard round the world" is part of a line in "The Concord Hymn," written in the 1830's by writer / philosopher Ralph Waldo Emerson for the dedication of a monument at the site of Concord's North Bridge.
>"Here once the embattled farmers stood,
>and fired the shot heard round the world."