In Animal Farm, what makes the Battle of the Windmill against Frederick's men seem different from the Battle of Cowshed?

The spirit
of the animals has grown grimmer and more despondent since the early days of the Battle of
Cowshed. The animals have had to build the windmill twice, since the first time it fell down,
and the loyal Clover has to mask her discontent by singing the "Beasts of England"
song when it occurs to her that a regime of hard toil and public executions was not what she had
envisioned when the animals first dreamed of owning the farm. Right before the battle,sold their
timber to humans for cash, an act violating the principles of animalism. By the time of the
Battle of the Windmill, the animals are tired and the early euphoria of their revolt has worn
off. Napoleon's only plan for defense, apparently, is to hope Pilkington and his men will help
them out, but Pilkington instead sends him a note saying "serves you right." The
animals are routed, retreating to farm buildings, until the humans dynamite the windmill. That
act rouses them to fury and they then drive the humans out. A difference showing how attitudes
have hardened is revealed whendeliberately breaks the heads of three humans with his hoofs and
doesn't mourn this, whereas he had been distressed when he accidentally killed a farmhand in the
long-ago Battle of Cowshed. The animals instinctively know they have lost this later battle
because of the destruction of the windmill. Even Boxer, realizing he is 11 and not as young as
he used to be, wonders if his muscles have what it takes to rebuild. (He nevertheless
"braced himself for the task.") Whenannounces the battle a great victory and Napoleon
orders a celebration, however, the animals succumb to the propaganda and begin to change their
thoughts.