Apple's revenue declined last quarter for the first time since well before the iPhone existed. Here's what happened, and what it means.

To no one's surprise, on Tuesday Apple posted its first quarterly decline in total revenue for the first time since 2003, ending a historic 13-year streak of growth for the technology company, which still remains the world's most valuable business.

The news was tempered by the fact that Apple predicted it would happen in its last quarterly report (Apple also foresees another drop in the next), but nevertheless, the end of over a decade's worth of amazing performance has people asking questions.

What Happened?

The company posted a year-over-year decline in revenue of about 13 percent, after bringing in $50.6 billion in revenue for the second quarter of 2016, along with $10.5 billion in profits.

The biggest reason was lagging global sales of the iPhone in the start of the year. For the second quarter of 2016, iPhone sales fell to 51.2 million units from over 61 million at the same time in 2015, and revenue fell by almost $7.5 billion from the previous year.

China was a particular rough spot for Apple's best-selling smartphone, as The New York Times noted. While up and coming Chinese competitors like Huawei and Xiaomi nabbed more customers from Apple, selling smartphones with similar design aspects and technical specifications but for hundreds of dollars less, the Chinese government hasn't helped Apple's move into the country recently, either.

In fact, last week two of Apple's digital services, the iBooks Store and iTunes Movies, were shut down by a Chinese regulator only half a year after they became available to customers in the country.

Overall, there has also been a slow-down in growth of the smartphone market in China, concurrent with the country's recent unstable economy.

At the same time, Apple's "tick-tock" iPhone product schedule inevitably led to fewer units being sold in China, and elsewhere.

The iPhone 6 and iPhone 6 Plus from 2014 was the first time Apple introduced iPhones with larger screens, leading to a huge increase in sales and pushing Apple's value into new world-record highs. The iPhone 6s and iPhone 6s Plus, with an almost identical design but only incremental improvements in other aspects, failed to wow customers quite as much.

Adding to the overall growth problem Apple experienced is the fact that the iPad peaked in sales years ago, and the Apple Watch seemingly hasn't taken up the slack.

What's Next?

Apple CEO Tim Cook told investors in a conference call that it had been "a challenging quarter," but said he remained optimistic about the future. The decline in iPhone sales, he said, was "a tough bar to hurdle, but it doesn't change the future."

"The future is very bright," he added. Investors are less confident about the immediate future, as much of Wall Street lowered expectations about Q3 2016 for the company.

But Cook pointed to the new iPhone SE, the latest model of Apple's smartphone that sports the company's traditional screen size, as a new growth category in the company's product line.

In addition, the company is pursuing the fast-growing smartphone market in India, and Cook said he believes that market is about where China was seven years ago: That is, ready to blow up with new potential Apple customers. Indeed, according to The Verge, iPhone sales grew 50 percent in India year-over-year.

The image of Apple's success, at least, has been tarnished in recent months, but the company is still one of the most valuable and profitable businesses in the history of business.

If this quarter was the beginning of some kind of "fall of Apple" -- rather than the "pause in growth" that Cook called it -- it's at least clear that Apple has a quite long way to go.