It seems like your question is predicated on a mistaken belief that cartographers just make maps of the world, and national boundaries. If that were the case, there would be very little work for cartographers to do.

In war, accurate maps are vitally important to any commander, so much so that the greatest commanders understand mapping terrain as well as they understand logistics, strategy, and tactics. Wellington carefully scouted the site of Waterloo and had topographical maps produced of the terrain as his army was passing through the area because he predicted accurately that Napoleon might bring him to battle before the Prussians could reinforce him, and he wanted to determine the most favorable positions in advance.

George Washington's early career was working as a land surveyor, mapping property for landowners such as Lord Fairfax. His skill as a surveyor and mapmaker served him well when it came to commanding in battle.

It's no accident that if you want to learn the skill and craft of mapmaking and surveying ground, you can not do much better than studying at a military academy. Cartographers do not close to shop in wartime. To the contrary, that's when they are vitally needed on a daily basis.

War is also an event that spawns innovations in cartography, as it frequently does in other fields. The Library of Congress has an excellent page on ways cartographers developed new mapping techniques in response to the Civil War.