In the American Revolution, the first real victory came at Trenton - and was not against the British, rather Hessian mercenaries. It was a tiny battle in comparison to modern ones - no Americans died and only a few of the enemy (including their Herr Oberst). But, the psychological impact was devastating. The British knew then, the Americans would not quit - and it became a practical matter of balancing more pressing needs at home against foreign adventures.

Even after getting reamed at Gettysburg, at Vicksburg, and after being besieged at Petersburg, the Confederates could have won simply by holding onto Atlanta and harassing Sherman until the fall elections of 1864. The invader has a massive onus - you would think we would have learned this lesson by now. The cretins in power are however incapable of drawing correct conclusions about anything. A more incompetent Executive has never existed.