What does the join or die mean

Widely considered America’s first political cartoon. During Franklin’s era, there was myth that a severed snake would come back to life if the pieces were put together before sunset.
The cartoon depicts the early American colonies as a snake divided into eight segments. Toward the head of the snake, “NE” represents New England, followed by “NY” (New York), “NJ” (New Jersey), “P” (Pennsylvania), “M” (Maryland), “V” (Virginia), “NC” (North Carolina) and “SC” (South Carolina). Even though there were four “New England” colonies, Franklin lumped them into one category to stress the need for colonial unity. At the time, the colonists fiercely debated expanding west of the Appalachian Mountains and fighting the French and their Indian allies.