Thorin's family mined and found a good deal of gold and jewels. They tunneled and made huge walls and workshops. Then, of course all of this brought in a dragon. And dragons love to steal gold and jewels from men, dwarves, and elves. They would steal from the North but gold was getting scarce up there with the dwarves going south or getting killed and the dragon destroying and setting fire to everything he saw made it worse. Then the most greedy and strong worm of them all, Smaug, began to travel south landed on a mountain in a spout of flame. Smaug then made his way down the slopes and began setting everything on fire. No one could escape this dragon and the river started to get steamy and fog destroyed most of the warriors. After that he went back to the town, stole all their wealth and kept for himself. After that no one ever returned to town either because they were dead or just gone.