The correct answer is - preserved the union.
The Civil War in the United States was a long and bloody conflict. It was between the North and the South, the two halves that had totally different policies and ambitions for the future. Despite the war being terrible and with lot of people who lost their lives, as all wars, something good came out of it too. The big positive of the Civil War was that it actually managed to preserve the unity between the states, thus creating the mighty United States of America, which eventually became the biggest power house on the planet.