Complex sentence: Stevens intentionally dropped the letter while walking among the pro-Clay Virginia delegation, with the result that the Virginians announced Harrison was their second choice, setting off a stampede for Harrison, who became the Whig nominee for president on the fifth ballot.
Split into simpler sentences: Stevens intentionally dropped the letter while walking among the pro-Clay Virginia delegation. After reading it, the Virginians announced Harrison was their second choice, setting off a stampede for him, and he became the Whig nominee for president on the fifth ballot.