Black*Smaug figured out the dwarves were the most powerful and amazing people in Middle Earth. It took him a while to hear about it because he actually had to listen to people instead of roaring at them, but eventually he overheard a couple dwarves boasting about how fucking bomb they were and he poked his huge head over a mountain peak.
"What? What's this? You think the Lonely Mountain is god?"
"The fuck?" said one of the dwarves. "No, that's not what I was saying."
"I'll conquer it!" Black*Smaug shouted. "I shall surpass this mountain!"
"Oh shit, wait," said the other dwarf, but Black*Smaug didn't hang around to reason with them, for Black*Smaug was impervious to reason. He zoomed off to the Lonely Mountain and beat the shit out of all the dwarves there, knowing he would be the tallest if he defeated this mountain. He totally did, too. That mountain was gutted by the time he was done with it.
"Yahooooo!" bellowed Black*Smaug. Then he fell asleep midair. He divebombed into a pile of gold, buried completely in shiny metal as he slept the sleep of a very stupid, very satisfied dragon.
It was one hundred and fifty years before the dwarves attempted to return to their godlike mountain.