The Heart of Azeroth is an artifact given to the player character from the world soul via Magni Bronzebeard. It is a necklace that can use the power of Azerite, the lifeblood of the embryonic titan Azeroth (See Plot, below). Azerite is similar in function to Legion's artifact power, in that it is gathered normally from playing the game and is used to upgrade an artifact; likewise, the Heart is similar in function to Legion's artifact weapons by having the capacity to be constantly upgraded. Unlike artifact weapons, however, the Heart is shared with all of the player's specializations and can empower all eligible pieces worn simultaneously.
I do not recommend going for TBC, although I remember Hellfire peninsula to be decent, everything else is rather slow. Instead go for WotLK, Borean Thundra gets you levelled very fast, and then you can head straight for Icecrown at 67, which is also insanely fast, although admittedly has a few elite quests. You can go to Sholazar Basin alternatively. 2 zones should get you 60-80 no problem.
World of Warcraft: Battle for Azeroth is the seventh expansion for World of Warcraft revealed at BlizzCon 2017 and announced for release on August 14, 2018. The Alliance, led by King Anduin and Genn Greymane, attacked Lordaeron, Warchief Sylvanas' base at Undercity, in response to the Horde burning down Teldrassil. The factions are at war. Between the Alliance-controlled Eastern Kingdoms and the Horde-controlled Kalimdor is the Great Sea. It is in this Sea that a majority of the expansion will take place.
When an allied race has been unlocked for a player, new characters from that race will start at level 20. If a player levels an Allied race from 20 to level 110 without using character boosts, they will be rewarded with a unique "Heritage Armor" for transmogrification that reflects the unique lore behind the race but is limited for use to that race. Doing the quests to unlock the allied races will also unlock the races' unique mounts for use by the characters of their faction. The void elves, Lightforged draenei, Highmountain tauren, and Nightborne, as races tied to the storyline for Legion, were made available with the preorder on January 30, 2018. The Dark Iron dwarves and the Mag'har orcs are made available upon completing the "War Campaign" in Kul Tiras and Zandalar and reaching Exalted with one faction's War Campaign reputation; the Kul Tiran humans and Zandalari will be made available later in the expansion. Game director Ion Hazzikostas also indicated that additional Allied Races may be available in the future.
Mag'har Orc Allied Race Leveling Guide (20-120) Dark Iron Dwarf Allied Race Leveling Guide (20-120) Void Elf Allied Race Leveling Guide (20-120) Best Void Elf Allied Race specs for leveling, efficient zones to level in, and overview of available classes and level 20 starting abilities. Level a Void Elf to 110 for a special set of cosmetic Heritage Armor. Nightborne Allied Race Leveling Guide (20-120) Best Nightborne Allied Race specs for leveling, efficient zones to level in, and overview of available classes and level 20 starting abilities. Level a Nightborne to 110 for a special set of cosmetic Heritage Armor.