Terraria is a long flat strip of land south of Minecraftia. In a strong contract to Minecraftia, it is mainly unsettled, with the largest towns havng only 10-20 people. The main reason is the myriad of powerful monsters that inhabit the region like creepers, harpies and rarely Slenderman.
However, Canada, Fuhur and Hyrule have large mining operations with the intention to take the Cobalt, Mythril, Titanium and Adamantite. Canada has also done research on Chest duplication in the area and why it works.
Terraria was discovered when Canadian ships were trying to go to Minecraftia to get diamonds, but were blown off course. They established a port on the western end, and soon Hylians and Uncarians began setting up towns as well. In 1734, Terraria became an independent nation (the smallest one).
In 1984 disaster struck. A Terrarian explorer ventured down to get a demon chest for duplication, but accidentally summoned the Wall of Flesh. He won, but ever since, the monsters of the region have become stronger.