<P> The decisive factor , in the fall of 1862 and increasingly thereafter was the Battle of Antietam and what grew out of it . Lee 's invasion was a failure at Antietam , and he barely escaped back to Virginia . It was now obvious that no final , conclusive Confederate triumph could be anticipated . The swift recession of the high Confederate tide was as visible in Britain as in America , and in the end , Palmerston and Russell dropped any notion of bringing a mediation - recognition program before the cabinet . </P>
which battle ended britain 's support for the south
Battle of Antietam