The siege of Yorktown, and the subsequent surrender of British forces to the revolutionists, seems almost accidental in light of all the events that had to happen at this precise battle to ensure Cornwallis' defeat. To be fair, some of what happened was due to sheer folly. For example, he slaughtered his own horses to avoid feeding them on the assumption that British ships would be available to take him back home (and I think we all know the saying about assumptions). He also sank his own ships in an attempt to block the revolutionists from advancing upriver. This maneuver confused me the most as you would think someone attempting to sail back to England would want to hold on to his ships. The poor weather as well as the size of the revolutionists' army, which was double the size of Cornwallis', contributed to his inability to retreat.

To be fair to Cornwallis, he could not possibly have known that the French would actually ally with the rebels. Nor could he have known that Washington had set up an elaborate ruse including troop movements and empty tents to make him think New York was the happenin' place to be in order to keep most of his ships out of the way. Likewise, he could not have known that Plymouth, while malaria infested, would possibly have not been the worst place for him and his troops to summer. Not only did Cornwallis not want to be in Plymouth, he didn't even want to be in Yorktown a town which reached its peak during the siege.
The final circumstance that Cornwallis could not have predicted was that, although he delayed fighting as much as possible on the assumption he would soon be relieved, Clinton would not actually arrive until one day after he surrendered. All of these situations combined actually made me feel a bit sorry for Cornwallis. He was being ordered by Lord George Germaine who stayed in England throughout the conflict, he was chronically undersupplied and popular sentiment was against him. There doesn't seem to be much in his favor aside from a vastly superior navy, as well as better weaponry (as long as it didn't fall into the hands of the rebels as some cannons did). For all that then English began the war thinking it would be brief, they certainly lost in a most inglorious way. Not that that negatively impacted Cornwallis' reputation; he went on to become governor- general of India twice and Lord Lieutenant of Ireland.

The English seem to have suffered from "It works on paper" syndrome in which the intended plans ought to work, but usually go terribly awry. The English assumed that most southerners would be loyalists due to their mercantile status. Trade with England was profitable and the areas of discontent had so far only occurred in New England. So, the idea was to cut off New England from the rest of the colonies to contain the rebels while acquiring supplies from Southern Loyalists. This worked about as well as when the same thing was attempted in 1607- in that it didn't. There were far more revolutionists in the south than previously supposed and they were not inclined to support Cornwallis. The fact that the colonists were in the habit of stringing up or driving out the loyalists certainly did not incline people to be overly vocal about their support of George III.

The English also seem to have counted on dealing mostly with the militia, which would have been to their favor. The militias were undertrained, underfunded and more likely to run back home since they fought in familiar territory. These would be the "farmers with pitchforks" Cornwallis was so contemptuous of (line courtesy of the second worst movie ever made). Our discussions today reinforced the idea that after the Battle of Saratoga, the war was a foregone conclusion. At the very least, Cornwallis' decisions combined with unforeseeable circumstances, made his defeat at Yorktown and near inevitability.