Can you identify any points where a different decision or course of action might have changed the historical trajectory of the Civil War?

There are many hypothetical situations in which the Civil War would have turned out differently. The first aspect to consider would be foreign involvement on the Confederate side. The war was so bloody that, early on, Britain and France nearly insisted on arbitrating between the two sides in order to stop the war. While the major powers of Europe maintained their cotton stores thanks to cotton production from their own colonies, it is interesting to consider that Britain and France were considering lending aid or even military support to the South in order to maintain textile mills.
Another thing to consider is that the Army of Northern Virginia had the war nearly won in 1861 with its victory over the Union Army at First Bull Run. If the Confederate Army would have marched the relatively short way to Washington D.C. and taken advantage of the shock in the capital, then that would almost certainly have ended the war. This scenario is not likely, however, as the Confederate army was disorganized after the battle and really could not follow up on its victory.
Another thing to consider is a Confederate victory at Gettysburg. Such a victory would have made outside intervention from Europe more likely and it could also make the Union government consider petitioning for peace. Lee's gamble to send George Pickett's division against the middle of the Union line was supposed to split the Union army. If this worked, then the trajectory of American history would be vastly different.
Finally, consider what would have happened if Lincoln would have lived. He could have changed his mind about going to Ford's Theater that night. If he would have lived, would he be able to pass his conciliatory reconstruction over the head of radical Republicans in Congress, many of whom never did warm to him? Would the nation be quick to forgive considering the war killed over six hundred thousand people? While I realize that this deals with the postwar world, it is potentially the most important hypothetical situation to consider.