Pokemon: By the Generations
The first Pokemon main series games — Pokemon Red and Pokemon Green in Japan and Pokemon Red and Pokemon Blue in the west — kicked off the entire franchise, establishing Generation I and bringing the first 151 Pokemon to the world. From here, PokeMania was in full swing, spawning a trading card game, anime series, family of games (main series and side games), manga, and much, much more. Following the success of everything in Generation I, the series would enter it's first subsequent generation in Gen II, starting with the release of Gold & Silver. From here, the world of Pokemon would expand more and more until taking over the entire real world. Here's a historic timeline of each major Pokemon generation over the years.
Note: This focuses on western releases.
Generation I
Debut Year: 1996 (Japan)/1998 (North America, Australia)/1999 (Europe)
Main Series Games: Red & Blue, Yellow
Major New Region: Kanto
New Pokemon Introduced: 151
Notable Mechanics Introduced: Basically everything! Including: evolution, battling, trading, Gyms, the Elite 4 and Champion, 15 types, Pokemon Professors, rival battles, HMs, weaknesses/resistances, Legendary and Mythical Pokemon, villainous teams (Team Rocket), Pokemon friendship, branched evolutions, side games
Generation II
Debut Year: 1999 (Japan)/2000 (North America, Australia)/2001 (Europe)
Main Series Games: Gold & Silver, Crystal
Major New Region: Johto
New Pokemon Introduced: 100
Notable Mechanics Introduced: day/night cycle, cross-generation evolutions, two new types: Steel and Dark, Pokemon genders and breeding, shiny Pokemon, Baby Pokemon, held items, Special Attack and Special Defense split, female player characters, character gear systems, event Pokemon, online capabilities, Battle Towers/facilities, Move Tutors, weather conditions in battle
Generation III
Debut Year: 2002 (Japan)/2003 (North America, Australia)/2003 (Europe)
Main Series Games: Ruby & Sapphire, Emerald, FireRed & LeafGreen
Major New Region: Hoenn
New Pokemon Introduced: 135
Notable Mechanics Introduced: Abilities, natures, Pokemon Contests, new villainous teams (Team Magma and Team Aqua), Secret Bases, Double Battles and Multi-Battles, Pokemon personality values, the modern Berries, wireless communication, Shadow Pokemon, running shoes, main series remakes (FireRed & LeafGreen), maximum EV threshold
Generation IV
Debut Year: 2006 (Japan)/2007 (North America, Australila, Europe)/2008 (Korea)
Main Series Games: Diamond & Pearl, Platinum, HeartGold & SoulSilver
Major New Region: Sinnoh
New Pokemon Introduced: 107
Notable Mechanics Introduced: three-dimensional overworld, the Physical-Special split, the designation of "status move" as its own category, Nintendo Wi-Fi Connection, off-game Pokemon storage (My Pokemon Ranch), the Sinnoh Underground, Pokeathlon, a new villainous team (Team Galactic), Arceus as the creator of the Pokemon universe
Generation V
Debut Year: 2010 (Japan)/2011 (North America, Australia, Europe)
Main Series Games: Black & White, Black 2 & White 2
Major New Region: Unova
New Pokemon Introduced: 156
Notable Mechanics Introduced: a region not inspired by Japan (Unova is based on New York), in-game seasons, Triple Battles and Rotation Battles, the Entralink and Pokemon Global Link systems, sprites that move constantly, infinite-use TMs, Pokemon Musicals and PokeStar Studios, an Elite Four that can be battled in any order, difficulty levels, a new villainous team (Team Plasma)
Generation VI
Debut Year: 2013 (Worldwide)
Main Series Games: X & Y, Omega Ruby & Alpha Sapphire
Major New Region: Kalos
New Pokemon Introduced: 72
Notable Mechanics Introduced: a new type: Fairy, the entire games being 3D, Pokemon Bank, Mega Evolution, Terrain, a new villainous team (Team Flare), player customization, the ability to walk in eight directions, mobile games (including Pokemon GO)
Generation VII
Debut Year: 2016 (Worldwide)
Main Series Games: Sun & Moon, Ultra Sun & Ultra Moon, Let's Go Pikachu & Let's Go Eevee
Major New Region: Alola
New Pokemon Introduced: 88
Notable Mechanics Introduced: Z-Moves, Ultra Beasts, replacement of HMs with Ride Pokemon, regional forms, the Island Challenge instead of Gym leagues, Battle Royal, SOS Battles, Poke Pelago and Festival Plaza, move effectiveness displayed in battle, free-direction movement, new villainous teams (Team Skull, Team Rainbow Rocket), Rotom Dex, the visibility of wild Pokemon on the overworld, co-op simultaneous multiplayer, Champion Title Defense battles,
Generation VIII
Debut Year: 2019 (Worldwide)
Main Series Games: Sword & Shield, Sword & Shield DLC: The Isle of Armor & The Crown Tundra, Legends: Arceus, Brilliant Diamond & Shining Pearl
Major New Regions: Galar, Hisui
New Pokemon Introduced: 96
Notable Mechanics Introduced: Dynamax and Gigantamax, the Wild Area, Pokemon Camp, paid Downloadable Content, Pokemon HOME, the Y-Comm, Max Raid Battles, a smartphone for the player, a new villainous team (Team Yell), marks and titles, the Champion Cup's replacement of the Elite 4, the inability to transfer in every existing Pokemon, many mechanics unique to Legends: Arceus (direct damage between player and wild Pokemon, move mastery, open-world expeditions, an existing region's presence in the past via player time travel, Noble Pokemon and their wardens, Pokedex research tasks, stealth mechanics, crafting, Action Order)
Generation IX (current)
Debut Year: 2022 (Worldwide)
Main Series Games: Scarlet & Violet, Scarlet & Violet DLC: The Teal Mask & The Indigo Disk
Major New Region: Paldea, Kitikami
New Pokemon Introduced: 112 (so far)
Notable Mechanics Introduced: the Terastal phenomenon, open-world gameplay, Paradox Pokemon, four-player multiplayer (Union Circle), a new villainous team (Team Star), Titan Pokemon, picnics and Herba Mystica, Tera Raid Battles, breeding via picnics, Poke Portal, manual activation of Trainer battles (removal of sightline battles), ecologically-similar Pokemon, gyms that can be challenged in any order
Pokemon: Game Rant Resources
At Game Rant, you can find a ton of resource, guides, walkthroughs, rankings, and more, for almost any modern-generation Pokemon game from Pokemon Unite to Pokemon GO. Consider this a branched directory of directories, leading you where you need to go!