During th civil war where was the capital of the US?
Washington, DC, same as today. When the US was created, Philadelphia, PA was the first capital, but by the time of the Civil War Washington had been the US capital for many years.
The capital of the US. during the Civil War remained Washington DC, just as it was during the outset of the war. However, Abraham Lincoln had to declare martial law in Maryland to prevent the state from seceding and joining the Confederacy. That would have left his capital surrounded by hostile territory and probably would have forced the US. government to relocate.
The US capital before, during and after the US Civil War was Washington DC. Although it practically bordered the Confederate state of Virginia, the Potomac River lay between the city and the nearest major Virginia town of Alexandria. During the war, its fortifications prevented any attempt by the South to capture it.