Despite there being many other causes that contributed to the loss, the driving reason was that Lee surrendered to General Grant because his regiments were completely surrounded by Union cavalry troops who arrived near Appomattox long before the confederate army arrived. Because of this they were able to effectively thwart any possibility of retreat from Lee's armies. They also took a large amount of confederate prisoners. Because of this, Lee was forced to acknowledge to General Grant that the Unionists had won the American Civil War.
