The "Union cause" refers to the efforts and motivations behind the Northern states during the American Civil War (1861-1865) to preserve the United States as a single nation. The Union, representing the federal government and its supporters, aimed to defeat the Confederacy, which sought to secede and form its own government. Key issues included the preservation of the Union, opposition to slavery, and the belief in a democratic government. Supporters of the Union cause believed in the principles of liberty and equality, as outlined in the Declaration of Independence. Prominent figures, such as President Abraham Lincoln, played crucial roles in rallying support for the Union, emphasizing the importance of maintaining national unity and the moral imperative to end slavery.