What cause the civil war to end?

The Confederate armies, running out of food and supplies, eventually surrendered to the larger, better-equipped Union armies. This occurred rather quickly after Union forces under General William T. Sherman cut a swath through the South on his March to the Sea (November-December 1864).

On April 3, 1865, the Confederate capital at Richmond, Virginia was captured and on April 9, 1865, Confederate commanding general Robert E. Lee surrendered to Ulysses S. Grant at Appomattox Court House. The remaining Southern armies mostly stopping fighting within the next few weeks.