The main issue of the American Civil War was linked with what?

Correct answer: Slavery and unity of the Union

The American Civil War was mainly connected with slavery and the preservation of the Union. The conflict between the Union and the Confederacy from 1861 to 1865 involved disputes over the expansion and future of slavery, the power of states, and whether the United States would remain one nation. As the war continued, ending slavery became a central Union purpose. Therefore, option A is correct. Mongol expansion, the Suez Canal, and Chinese unification were unrelated subjects and cannot explain this war.

The phrase “main issue” should not be reduced to only one political detail. Slavery was the deepest underlying conflict, especially over its expansion into new territories, while secession threatened the country’s unity. President Abraham Lincoln led the Union during the war and later issued the Emancipation Proclamation. These facts connect the event with both slavery and preservation of the Union. Thus the combined wording in option A is more complete than either an unrelated alternative or a single oversimplified label.