And yet that's (the Civil War) what made us a nation. Before the war, people had a theoretical notion of having a country, but when the war was over, both sides knew they had a country. They'd been there. They had walked its hills and they had tramped its roads. They saw the country and they knew they had a country. And they knew the effort that they had expended and their dead friends had expended to preserve it. The war made their country an actuality.
Before the war, it was said, "The United States are..." Grammatically, it was spoken that way and thought of as a collection of independent states. After the war, it was always, "The United States is..." -as we say today without being self-conscious at all. And that sums up what the war accomplished. It made us an "is".