The global population has exploded.
In 1998, the world was gearing up for a huge milestone — the global population was sitting at 5.9 billion, and the following year would finally break the 6 billion mark.
Fast forward 20 years, and the world's population is estimated at 7.6 billion. Meanwhile, the US population has jumped from about 276 million to 327 million in the same time frame.
And more and more people are living in cities.
Another huge population shift is happening in our cities. Twenty years ago, less than half of the world's population lived in urban areas, according to The World Bank.
But in 2007, the world's urban population eclipsed the 50% mark, and today 55% of people live in urban areas. That number could reach as high as 66% by 2050, putting further strain on cities that are already being pushed to the brink, according to a UN report.
Buildings are reaching previously unimaginable heights.
In 1998, the brand-new Petronas Twin Towers in Malaysia became the tallest buildings in the world, standing at 1,483 feet and edging out Chicago's Sears Tower by just 33 feet.
Since then, there has been an explosion in the number of skyscrapers worldwide — and they keep getting taller. The current title-holder, the Burj Khalifa in Dubai, stands more than 1,000 feet taller than the Petronas Towers, which have fallen all the way to 15th on the global list.
There are seven more skyscrapers under construction — all in Asia — that will top out at over 1,600 feet. The tallest among them, Saudi Arabia's Jeddah Tower, will be the first building to ever surpass the 3,000-feet mark. Collectively, the increase in skyscrapers is a symbol of Asia's emergence onto the international business stage, as The New York Times put it.
The internet has changed the way we do … everything.
It's hard to imagine a world without the internet today, but that wasn't the case 20 years ago. In 1998, only 41% of American adults were online, compared to 89% today, according to the Pew Research Center.
1998 was also the year a little company called Google was born, although back then, it looked a little different than it does now.
Today, the internet has transformed virtually every aspect of our lives, from the way we communicate to to how we consume news, shop, navigate, and entertain ourselves.
Social media has taken over.
One of the most influential applications of the internet is social media. Today, more than two thirds of all Americans are on Facebook, the most popular social media platform, and in three years there are estimated to be more than 3 billion social media users overall around the world.
That's a far cry from how things were 20 years ago, when the closest thing there was to modern-day social media was AOL Instant Messenger and do-it-yourself Geocities webpages.
Phones are a virtual necessity, and almost everyone has one.
Like other forms of technology, cell phones have become increasingly ubiquitous over the past 20 years — just look at how they've evolved over the years.
Cell phone ownership is at an all-time high of 95% in the United States, compared to under 60% in 1998. Meanwhile, 77% of Americans own smartphones, which have transformed phones from mere communication devices into full-fledged handheld personal computers.
September 11 had a profound impact on our society.
It's hard to understate the effects the September 11, 2001 attacks had on the world.
For one, they led to resentment toward Arabs and Muslims in the Western world that arguably hasn't subsided in the years since. The attacks also gave way to wars in Iraq and Afghanistan — the latter of which is still ongoing — that have harmed America's reputation abroad. The airline industry has also undergone dramatic changes because of the attacks, and 9/11 even changed the way we talk.
But perhaps the biggest change in the world is how people think of terrorism itself. Before the attacks, the US government prosecuted terrorism suspects in civilian criminal courts, not military tribunals, and terrorism certainly wasn't the focal point of political campaigns and 24-hour news coverage.
The effects of September 11 are still unraveling, but they've already made a huge mark on many aspects of life today.
People no longer believe in banks.
The 1990s saw the largest continued economic boom in American history, one that lasted from 1991 to 2001.
Fast forward to today, and trust in financial institutions has never been lower, with just 8% of Americans reporting they had faith in them in 2016, according to Time. Younger generations are especially distrustful of banks.
The global financial crisis of 2008 contributed to people's perceptions of corporate greed and corruption, and the Occupy Wall Street movement three years later shined a light on income inequality — two factors that have changed the way we look at our financial system forever.
Self-driving cars have finally arrived.
In just a couple of decades, self-driving cars have gone from a distant dream to a reality.
The idea of an autonomous vehicle wasn't completely crazy in the 1990s, though. Self-driving prototypes had been developed since the 1970s, and in 1995, researchers from Carnegie Mellon University developed a car that could steer by itself, although a driver still had to operate the brakes and hand throttle.
Nowadays, companies like Tesla, GM, Ford, Uber, Google, and Apple are all developing their own self-driving vehicles, and they're already being tested in major cities around the countries.
Climate change is becoming a grim reality.
Researchers have been aware of the Earth's changing climate for decades, but the devastating effects have become especially apparent in recent years. Weather-related records are being shattered at an alarming pace — the past four years were the hottest in recorded history, and the past few years have given us some of the hottest individual months as well.
Meanwhile, the effects of climate change are already a reality for people from island nations in the Pacific, who are having to evacuate and relocate as entire towns become submerged underwater.
Environmental issues play an increasingly large role in international politics, most recently evidenced by the Paris climate accords of 2015.
And numerous social issues are finding their way into the spotlight.
Each generation brings new social issues to the forefront, and many of them have come to a head in recent years.
Groups such as Black Lives Matter have highlighted inequality in the criminal justice system, and the #MeToo movement that sprung up last year put the spotlight on women who have endured sexual harassment and abuse in all areas of life.
Meanwhile, LGBT-rights advocates have pushed for increased rights and legal protections, and in 2015, the US Supreme Court legalized gay marriage in all 50 states.
