New York City and London are sister cities, allies and neighbors who only happen to be separated by an ocean. Their inhabitants speak the same language, for the most part — ahem, it's a sweater not a jumper.

So why go through all the trouble of hosting separate fashion weeks in both New York and London, or in any respective city at all?

The answer is simple. While their DNA is similar, their styles are practically polar opposites.

As a former New Yorker, writer and stylist Laurel Pantin now calls London home. She tells Mashable, "In my opinion, New York fashion week is really representative of the way people these days are shopping. It's a good view of the way people actually dress. It's more commercial, polished, and probably more conservative than London. London fashion is a lot more experimental and out there than New York. You see things in London that are completely unwearable, and will likely never, ever, ever go in to production in any form, but that are really inspiring and fun. There's definitely more of a freak flag fly vibe in London that I love!"

A look from Ralph Lauren's spring 2015 runway show Image: Courtesy of Ralph Lauren/Ashby Group

Famous designer names like Ralph Lauren, Calvin Klein, Tommy Hilfiger and Michael Kors are synonymous with American fashion royalty. Their classic sportswear aesthetic is woven tightly into the nation's history and into its department stores.

New York Fashion Week flaunts this American classic aesthetic. The runways crawl with commercial pieces and wearable separates, ready to jump directly from the runway into your closet. The aim is to open store buyers' check books and land on magazine editor's wish lists. It's not unusual for runway attendees to utter, "I need that look now" or "That would be perfect for my event next week."

Even the city's edgier brands like Alexander Wang stay true to timeless silhouettes, adding striking colors or mesh fabrics for a taste of downtown grit.

A look from Alexander Wang's spring 2016 collection. Image: Corbis/Jason DeCrow

Still, such details are tamesauce compared to the frisky flair of British fashion.

Vivienne Westwood is one of the UK's most established brands, known for pioneering modern punk. Her spring '16 show this season was held in a venue labeled as an “Alien Sex Club.” Inside a soundtrack of police sirens blared as models dressed in eclectic looks and descended the catwalk with the designer while raising signs of protest.

Vivienne Westwood walks the runway with a mob of models. Image: Tristan Fewings

The underlying attitude at this presentation is replicated throughout the rest of the city. There's a freedom at the London shows to be whoever you want to be without consequence.

Historic roots

Functional fashion has pumped through America's veins for decades. From Levi's blue jeans born in 1873 out of a need for a sturdier work pant to the cowgirl ruggedness of the wild west, the essence of American fashion has always mimicked the spirit of its people. The idea that if you work hard you have the freedom to achieve your dreams is the thread that is woven throughout the country's style history.

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Esther Allen fishes for trout in String Lake in Jackson Hole in 1948. Image: ALFRED EISENSTAEDT/THE LIFE PICTURE COLLECTION/GETTY IMAGES

In the 1940s, World War II forced many women to roll up their sleeves and step into jobs traditionally held by men. Images of Rosie the Riveter were created to encourage women and spur them to action. The fictional character's blue button-down work shirt and red bandana became both a cultural and fashion icon.

Later, actress and bombshell Marilyn Monroe further solidified the ease of American beauty with classic turtlenecks and streamlined dresses that showcased her hourglass shape.

Marilyn Monroe in 1953 Image: Getty/Alfred Eisenstaedt / Contributor

Ten years later the nation saw the rise of first lady fashion as Jackie Kennedy entered the White House and the limelight. Her classic style of simple separates and shift dresses created a phenomenon mimicked by women around the world.

Style & Grace! #fwstyle A photo posted by Alexandria Wunmi Alli (@fwstyle) on Aug 26, 2015 at 4:19am PDT

Cindy Crawford, Naomi Campbell, Linda Evangelista and Christy Turlington became the plumb lines for beauty in the '80s and '90s, when the supermodel was born. Their easy slip dresses, structured blazers and high-waist jeans quickly became wardrobe staples.

Cindy Crawford, Pepsi commercial, 1992 pic.twitter.com/8KicnDDeiK — Hashim AbdelHamid (@hashoooo) August 14, 2015

But traveling from the Big Apple to London, especially during fashion weeks, is like walking out of Barneys department store and into Willy Wonka's world of whimsy. If American fashion is rooted in tradition and an entrepreneurial spirit, then British style is fueled by a wild child air of rebellion.

This British fashion liberation began in the 1960s. Up until that time, American and British styles were more or less comparable. Known for its bustles, corsets and respectable silhouettes, UK style played it fairly safe. The invention of the mini skirt by Mary Quant in 1964, however, caused the entire world to look to London as a trendsetter. The sky-high hem length sat six or seven inches above the knee and was a shocking departure from the full skirts worn in the '50s.

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English models like Twiggy and Jean Shrimpton also stormed onto the scene, redefining standards as their waif-like frames replaced curvaceous models. English designers began to experiment with wacky colors, textures and unconventional materials like lurex threads and PVC.

Twiggy modeling a lurex look in 1967. Image: Globe Photos/ZUMA Press/Corbis

Once UK brands got a taste for innovation, they never looked back.

Fast forward to modern day. This most recent season was full of the fantasy and excitement fashion fans have come to love.

Exaggerated puffed and bold prints at J.W. Anderson's spring 2016 show Image: Fashion GPS

Acclaimed as one of London’s “most innovative and forward-thinking brands,” J.W. Anderson first landed on the fashion week calendar in 2008. The label is known for its fluidity between masculine and feminine elements.

Eccentric makeup made models unrecognizable on the Gareth Pugh runway. Image: Fashion GPS

Presenting in London’s Soho on a Saturday night, Gareth wanted his collection to capture the neighborhood in its disco glory days. He likened the experience to “falling down a rabbit hole” and producing “feelings of euphoria, of danger and of possibility.

Ashish has quickly become one of London’s most popular brands. The lively and carefree spirit that is infused in the designs was replicated on the runway, as models scooted on skateboards and tossed glitter into the audience.

So much fun yesterday with @nowai_swrdwn and @jayboogie #ashish #ss16 #lfw repost from @voguediary A video posted by ASHISH (@ashish_uk) on Sep 23, 2015 at 2:32am PDT

Marques Almeida is known for designs that are rough around the edges. The creative duo produced the line of shredded denim and burlap in direct opposition to the prim and proper party dressing that was permeating the London scene. They desired to provide nationals with a brand that represented the real fashions on the street.

Signature frayed edges from Marques Almeida Image: Fashion GPS

While their artistic forms couldn't be farther from each other, both New York and London are important pillars in the fashion community.

The business portion of the industry thrives on wearable designs that start in the Big Apple and sell out at retailers across the world. New York is the practical city, producing finely tailored garments that insiders want to snatch right off the runway. London is its crazy cousin, infusing theatrical fantasy into a society that sometimes needs to be reminded that fashion is meant to be fun.