Most non-Chinese don't trade stocks in China, but the continuing crash in the Shanghai market still threatens to change their lives. The challenge is that China is the world's largest exporter ($2.2 trillion worth in 2013) and second-largest importer ($2 trillion), so its struggles are potentially the world's problems.
Compounding the importance of China's sheer size is the fact that its nominally Communist government is much more opaque than in fully-developed nations, and that its policy response to the fast-moving bear market has been clumsy.
Moves like today's cuts in interest rates and reserve requirements for banks have been met with derision and accusations that the moves show desperation, thanks in part to earlier steps to cope with stock selling by closing markets and encouraging state-owned pension funds and enterprises to prop up stock prices with mass purchases.
"Who on God's earth thinks it's an appropriate measure to close trading for 70 percent of the market?" Janus global asset-allocation head Ashwin Alankar said. "The People's Bank of China has lost its credibility."
China's woes threaten the U.S. and the world in many more ways than just the five listed here, but here are some of the big issues. The hitch is that many of the potential trouble spots have been looking very healthy even until very recently. It's too soon to know whether the financial markets' problems will quickly spread into the real economy, as happened in 2008 in the West, or stay relatively contained as they did when the Internet bubble burst in 2000, spurring only a relatively-modest slowdown.
1. U.S. exports are at risk.
The U.S. exported $123.7 billion worth of goods and services to China last year, according to the Census Bureau, up 1.6 percent from 2013. That's about 0.7 percent of U.S. gross domestic product—not a huge problem, but potentially an exposure that could crimp U.S growth by a few tenths of a percentage point if exports drop very sharply.
The three biggest categories of U.S. exports to China were soybeans ($14.5 billion), aircraft and parts ($13.9 billion) and cars ($11.2 billion), comprising almost a third of the total. But there are at least 26 other industries that export at least $1 billion worth of stuff to China—from $5 billion of semiconductors to $1.1 billion of cotton.
In context, U.S. exposure isn't all that large; it's about 6 percent of China's total imports. Japan, South Korea and "other Asia" each account for more of China's imports than the U.S. does, according to MIT's Observatory of Economic Complexity.
Read MoreCramer: What China rate cut means
And China's biggest import is crude oil, at 14 percent of its total. Since very little U.S. crude is exported—it's generally illegal, but there are exceptions—China's biggest trade partner for oil is Saudi Arabia. All of these countries could be hurt more, especially with Saudi Arabia already scrambling to cope with collapsing oil prices.
2. Some big-name U.S. companies are exposed.
Take GM. The automaker sold more than 3.5 million vehicles in China last year through different joint ventures with local companies. Last month it said that it's investing $5 billion in new lines of cars being tailored for developing markets led by China and Brazil. GM claims it has nearly 15 percent of the China market, and gained market share in the second quarter. Retail sales in China dipped 1.4 percent during the quarter, but wholesale sales were up 7 percent as some cars made in China were exported.
As for Boeing, experts told the Washington Post the long lead times for aircraft orders will insulate the aerospace giant from major effects for some time. Boeing shares are down more than 10 percent in the last week and are roughly 19 percent off their 52-week high, but Boeing today raised its 20-year outlook for sales to China by 5 percent, to 6,330 aircraft worth $950 billion.
"Despite the current volatility in China's financial market, we see strong growth in the country's aviation sector over the long term," Randy Tinseth, vice president of marketing at Boeing Commercial Airplanes, told reporters in Beijing, according to Reuters.
Just like Boeing, Apple is fighting back against the perception that sales will soon be hit by softer demand in China.
"I get updates on our performance in China every day, including this morning, and I can tell you that we have continued to experience strong growth for our business in China through July and August," Cook said in an email to CNBC's Jim Cramer yesterday. Apple shares briefly rallied on Monday on the Cook email, but it wasn't until Tuesday that investor momentum in Apple shares was sustained, with the stock up 5 percent amid a broad tech sector rally. Apple shares are still down 18 percent since its July 22 earnings report.
Caterpillar has said the dollar's strength has hurt sales, raising fears that the more-recent devaluation of China's currency will add to the pain. United Technologies fell 7 percent the day it announced weak second-quarter earnings last month, blaming currency issues and the China slowdown.
3. Commodities markets are getting hit hard.
If China's real economy runs into a significant slowdown, commodities producers would feel the pain more directly than almost anyone— since China imports nearly all of its oil and coal and tens of billions of dollars worth of foodstuffs. But most of that would be felt outside the U.S., where the direct impact would be modest.
China's oil consumption growth would be likely to slow, as would its purchases of coal. Its market woes are one reason oil prices have hit a seven-year low. But these would not be huge problems for U.S. producers—less than 1 percent of imports by the four top Asian coal-burning nations come from the U.S., according to the U.S. Energy Department, and only $40 million of U.S. coal went to China last year. The U.S. sent $1.65 billion of finished petroleum products to China.
More important commodities exports from the U.S. to China include lumber, soybeans and copper. About $6 billion of wood and wood-related products move to China from the U.S., along with $2.9 billion of copper. Copper is down about 17 percent since June, and soybeans are off 14 percent.
4. Smaller Asian nations and markets, are heavily exposed to China.
China is a huge trading partner for most of Asia. It takes more than 10 percent of the exports from Japan, Korea, Singapore, Malaysia and Indonesia. Almost 30 percent of Australia's exports, led by coal, go to China. The breadth of China's reach is striking: It accounts for more than 10 percent of exports from countries as far away as Ethiopia, according to MIT, and nearly 20 percent of Saudi Arabia's exports.
Markets in most of these nations have been hit hard. Malaysian stocks hit a three-year low this week before beginning to rebound.
5. U.S. companies that cater to Asian tourists could feel the burn.
Walk around big shopping districts in the U.S. and the impact of Asian tourism is often palpable, as visitors wheel suitcases around to high-end shops and outlet malls alike.
—By Tim Mullaney, Special to CNBC.com