In The Patriot starring Mel Gibson, General Cornwallis is based on a real character of the same name, from The American Revolution. The real-life Cornwallis was admired by his men for his bravery and did not spend his time far away from the front line, working on tactical maneuvers, but was often side-by-side with his men. One of the differences with his on-screen character relates to a truce, such as the one with Benjamin Martin (played by Gibson), which never took place historically. In the movie version, Cornwallis is contemptuous of Colonel Tavington, who is loosely-based on Lt General Banastre Tarlton. His cruelty does not go unnoticed by Cornwallis but Cornwallis does not impede Tavington or his methods. In reality, there is no evidence that there was such animosity between the two.
The comments that Cornwallis, in the movie, states "Everything will change...everything has changed" relate to the recognition by Cornwallis that this is a turning point and that the British cannot succeed against the patriot forces. He is acknowledging the changing face of war and how these men, who are not trained military officers or soldiers, are able to undermine the might of the British Empire. These very men who are farmers, with no bloodline to speak of, bring the issue of superiority into question. Cornwallis felt superior against what he saw as essentially illiterate men. He suggests, through his remark, that he wonders how they will be able to govern effectively without the knowledge and superior education of the British aristocracy.
He is highly embarrassed by his defeat at Yorktown and sends his deputy in his place to the surrender ceremony. In actual fact, the real Cornwallis was absent from the surrender at Yorktown, apparently due to illness but was not disgraced by his surrender and went on to an illustrious career after his return to England.