Usually, <em>a disease is considered pandemic</em> when it crosses international borders. A disease that does not cross international borders is an epidemic. An example of a pandemic would be the Black Plague (also called the Black Death or the Bubonic Plague), which <em>killed most of the population of Western Medieval Europe.</em>
Hope this helps!
D. The British Army thought it would be too challenging to fight across the Appalachian Mountains.