Manifest Destiny was used by John L. O’Sullivan as an expression of territorial expansion. It started on an Anglo-Saxon goal to spread their civilization on North America.
McClellan discovered General Robert E. Lee's battle plan.
Obviously, infiltration and access to battle plans allow for the opponent to figure out what their opponent's plans are, thus giving McClellan the victory at Antietam.
Hope this helps!
<span>an official order or instruction to do something</span>
