Final answer:
The incident near present-day Uniontown, Pennsylvania, where George Washington commanded fire on French soldiers, initiated the French and Indian War, depicted through the personification of Uncle Sam in political cartoons.
Step-by-step explanation:
The event that occurred where Uncle Sam is depicted in various historical cartoons, signaling the start of the war, refers to the shooting on French soldiers by George Washington near present-day Uniontown, Pennsylvania in May 1754. This event triggered the French and Indian War, which also marked the beginning of a series of imperial conflicts between Britain and France. Uncle Sam is an iconic representation often used to personify the United States and its government, representing the nation's involvement or stance in certain historical events, as depicted in political cartoons symbolizing various wars and political situations including World War I, the Spanish-American War, and the French and Indian War.