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Minimalism and Grunge were really the two biggest movements of the early to mid 90's. They really changed the course of fashion at the time. Heroin chic kind of tied into this as well, and there's a great thread on it
here.
From the mid-late 90's it was all about the
retro reinvention thing. Think revamped 60's and 70's...flared trousers, platform shoes, retro wallpaper prints, disco, luxe-hippie, oversized "Jackie" sunglasses, embellished denim and logomania. A move towards punk/gothic style began in a more underground way around this time.
Major trendsetters of the decade were Prada, Tom Ford for Gucci, Marc Jacobs, Dolce and Gabbana, Alexander McQueen, Helmut Lang, Calvin Klein and Donatella Versace.
Into the 2000's the 70's disco/glam spirit lingered for a little bit and gradually designers began looking at the 80's instead.
s/s 2001 was full of
80's power dressing references. Sharp lines, patent leather/rubber, exaggerated corsetry, dolman sleeves, sequins, tight fittted skirts, stilletos, punk, ripped up and embellished jeans and tops, mid 80's prom dress looks, military tailoring.
Then with
f/w 01 everything changed. Designers were moving towards the
peasent/bohemian trend that would be a dominant force for the next few years. Off the shoulder "peasent" blouses, tiered flamenco style skirts, rich embroidery, ruffles, looser shapes, billowing caftans, printed chiffon, raw edged fabric treatments. That trend held strong until f/w 02.
F/w 03 saw a major change in spirit, with a war brewing overseas, things became more aggresive, more protective and more restrained then they had been. A lot of references to the 40's and the 80's. Tailored silhouettes, corseted waists, deep jewel toned colors, stockings. It was all very grown up and started the
Ladylike trend that would last for the next 2 years.
Designers continued to reference different eras for the next few seasons, namely the 20's and 30's glamour,
the mid 60's Mod,
the 70's bohemian (again),
Lolita inspired looks (babydoll dresses, mary-jane flats), and
80's New Wave.
Keep in mind that, even though I'm only referencing high fashion here, every single trend I've mentioned has trickled down into the mainstream wardrobe at some point.
Big names: Galliano for Dior, Tom Ford for YSL and Gucci, Prada, Marc Jacobs, Nicolas Ghesquiere for Balenciaga, Olivier Theyskens for Rochas, Alber Elbaz for Lanvin, Stefano Pilati for YSL (2005 and later), Christopher Kane, Proenza Schouler, Phoebe Philo for Chloe, Karl Lagerfeld for Chanel and Fendi.
I'd say study Style.com's archives from 2000 on and you'll get a real feel for what I'm talking about here. I put all of the key trends in bold.