What is the difference between Diablo 3 and Reaper of Souls?

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Diablo 3 is a game developed by Blizzard and was released in 2012. It released with the following classes:

• Barbarian
• Demon Hunter
• Monk
• Witch Doctor
• Wizard

Reaper of Souls was an expansion for Diablo 3 that was released in 2014. It added the following to the game:

• The Crusader class;
• Enchanting and Transmogrification via Myriam the Mystic;
• Clans and Communities;
• New loot system that changed how primary and secondary stats worked, as well as introducing legendary affixes.
• The removal of the Auction House;
• New difficulties following the Torment system, which gave a gradually increasing difficulty level with accordingly better rewards;
• Adventure Mode, which changed the whole format of the end-game and introduced Nephalem and Greater Rifts to the game.

Beyond this, the only other expansion that Diablo 3 has seen is the Rise of the Necromancer pack, which added the Necromancer class.