So how did Drago Bludvist manage to control an Alpha dragon? We see that he uses intimidation and fear to break other dragons, but an Alpha is the size of a small mountain. Even with his staff (which I assume he uses to make himself seem even larger and more intimidating) the Alpha should have eaten him.
SOME GOOD 'OL BOOK TRAINING
Actually, I've had some loose theories on the powers of humans. Of our minds and voices against dragon. It's like Drago said… "Power of Will". Humans have great will power, if nothing else. (We were kinda shorted on the physical attributes… mental is where we thrive).
There's also a possibility that the alpha was much younger when Drago got to him.