The major event associated with the phrase "the shot heard 'round the world" is the Battle of Lexington and Concord, which marked the beginning of the American Revolutionary War on April 19, 1775. This phrase captures the significance of the initial skirmish between British troops and colonial militia, symbolizing the start of the colonies' fight for independence from British rule. The battle marked a turning point in American history, as it galvanized colonial resistance against perceived tyranny. It inspired widespread revolutionary sentiments and ultimately led to the declaration of independence and the formation of the United States.