The Union had about 60,000 soldiers and the Confederates had about 21,000 soldiers.
Under the ‘umbrella’ of “Battle of Bentonville” there were 2 other small battles: The Battle of Averasborough and the Battle of Wyse Fork
General Johnston did a lot of ambushing in this battle, since that’s how the whole thing started.
Sherman’s army was split up into two wings/groups, and when attacking one of those wings, General Johnston thought that he attacked all of his army when it was only a piece of it all underestimating the union.