The abuse of power is foreshadowed several times in Animal Farm.
First of all, you've got Napoleon. The name in itself is foreshadowing. Napoleon, the man, was an ignoramus who wanted nothing more than power. He didn't really care about the people he stepped all over to get it, so long as he got it. Napoleon, the pig, is eventually brandished as having a personality all too similar to that of the man.
Then there's the AWOL milk incident. It's obvious that the pigs did something with it:
"'Never mind the milk, comrades!' cried Napoleon, placing himself in front of the buckets. 'That will…