What exactly did Benedict Arnold do that made him a traitor ?

Question

I was just wonderin' b/c I found out a while ago that I'm related to him in some weird way.

Answer 1

treason
http://www.ushistory.org/valleyforge/served/arnold.html

Treason is any attempt to overthrow the government or impair the well-being of a state to which one owes allegiance; the crime of giving aid or comfort to the enemies of one's government.
It is a serious crime, and if convicted, you can be put to death!
In 1780, Benedict Arnold negotiated with British General Henry Clinton to hand over the American fort at West Point, New York to the British for 20,000 sterling (about $1,000,000 today). His plans were discovered when his courier, British Major John André, was captured with incriminating documents. The capture of John André was considered so significant that a special award, known as the Fidelity Medallion, was created by the Continental Congress for those who had participated in John André's capture. http://www.whatis.tv/Benedict_Arnold.html

hope this was a little more informative