Short answers, pulled from the story.
The 36-page Volume 1: Men & Magic pamphlet appeared in 1974 as part of the original Dungeons & Dragons boxed set. This slim booklet contained twelve pages describing individual spells that referenced earlier Chainmail materials for duration and range details.
Gary Gygax wrote in 1976 about the dangers of unrestrained magic in campaigns stating that D&D quickly degenerates into a weird wizard show if left unchecked. He argued that players get bored quickly without restraints on magic users to balance the overall game against other character types.
Eight classic schools of magic exist in Dungeons & Dragons including abjuration, alteration, conjuration, divination, enchantment, illusion, invocation, and necromancy. Each spell belongs to one of these eight schools established in Advanced Dungeons & Dragons where specialization was formally introduced in the 1989 Player's Handbook.
In the Dark Sun campaign setting arcane magic draws power from life force of plants or living creatures causing environmental harm while Wizards record spells using string patterns and complex knots instead of paper pages due to resource scarcity. In Forgotten Realms the Weave serves as source for both arcane and divine spellcasting within that world protecting the world from unrefined dangers.
The d20 System published in 2000 by Wizards of the Coast formed basis for third edition Dungeons & Dragons rules. Third edition introduced non-memorizing sorcerers while 3.5e added at-will warlocks changing Vancian assumptions before fourth edition released in 2008 added unique powers to every class focusing on party roles.