Answer:
If the Border States (states that bordered both the North and South during the American Civil War) had left the Union during the Civil War, it is likely that Washington D.C., as the nation's capital, would have been surrounded by Confederate territory. This would have posed a significant threat to the city, as it would have been vulnerable to attack and occupation by Confederate forces.
In fact, there were several instances during the Civil War where Confederate forces advanced towards Washington D.C. and threatened the city. The most notable of these was during the First Battle of Bull Run in 1861, where Confederate forces under General Stonewall Jackson came within striking distance of the city before ultimately being turned back.
If the Border States had seceded and joined the Confederacy, it is possible that Washington D.C. would have been cut off from the rest of the Union, making it difficult for the federal government to function. The loss of the capital would also have been a significant blow to the Union's morale and international standing, as it would have signaled a major victory for the Confederacy.
Fortunately, the Border States remained loyal to the Union during the Civil War, and Washington D.C. was ultimately protected from Confederate occupation.
Step-by-step explanation: