Nothing spooked the markets in 2017, with stocks experiencing record low volatility. However, with mounting geopolitical issues, political uncertainty in the United States and rising interest rates around the globe, this year could see many more ups and downs.

What could impact markets in 2018? Here are six issues that investors should be paying attention to as they invest in the months ahead.

For the last several years, central banks around the world have engaged in quantitative easing, interest-rate reductions and a general loosening of monetary policy. That’s already reversing in the United States, which raised its overnight rate three times in 2017, to between 1.25 percent and 1.5 percent, but in other developed nations rates remain at ultralow levels. For instance, Sweden still has a negative interest rate of minus 0.5 percent.

That’s likely to change in 2018, says Jeff Knight, Columbia Threadneedle Investments’ global head of investment solutions and co-head of global asset allocation. Many people expect the European Central Bank, the Bank of Japan and the Bank of Canada to raise interest rates at some point in 2018, while Bank of England may raise its rate, too. “Other central banks are a year or two behind the Fed in the cycle,” he says.

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While rate rises can be a sign of economic strength, having too many hikes too quickly could send markets into a tailspin. Knight will be keeping a close eye on long-term government bond yields and whether the yields on those instruments invert, meaning they fall below short-term bond yields. That would happen if investors believed that monetary policy was becoming too tight. As of now, the 30-year U.S. government bond has a 2.9 percent yield, while the 5-year U.S. government bond has a 2.4 percent yield.

“If investors believe there’s a deflation risk with tightening or that it will choke off economic growth, then we could see that inverted yield curve,” he says. “Too much tightening could become a growth headwind. It’s what happened in 2006 at the end of a long series of Fed rate hikes.”

North Korea may now be sending athletes to the Winter Olympics in South Korea, but the threat of war with America remains. While global stock markets haven’t reacted much to a potential nuclear fallout, conflict continues to be a risk, says Tim Courtney, chief investment officer at Exencial Wealth Advisors, an Oklahoma City-based financial advisory firm.

While he doesn’t think the two countries will come to blows, it’s impossible to predict just what Kim Jong Un and Donald Trump will do or say next. If something changes, such as a more threatening missile test from North Korea, then markets could react. And if stocks do fall, then investors should be concerned.

“The market thinks that war with North Korea is not going to happen,” says Courtney. “But if we saw an announcement or test that did move the market, then I would look at that and say someone knows something and it doesn’t look good.”

Will Trump scrap NAFTA? Will he engage in a trade war with China? Those are the questions many investors are likely wondering, and as with most things Trump, it’s difficult to know whether his antitrade Tweets and talks are genuine or if they’re a negotiating tactic.

If Trump does start a trade war with other countries, then investors should watch out. On Jan. 11 Canada filed a trade complaint with the World Trade Organization over its and America’s ongoing softwood lumber issues — a move that could ratchet-up trade-related tensions. And while Trump did tell the Wall Street Journal that same day that NAFTA is not yet off the table, exiting from the deal is still a possibility.

If that happens, North American stocks will likely tumble, especially among the sectors that NAFTA impacts most, like agriculture and autos, says Mandana Hormozi, a portfolio manager with Franklin Mutual Series. “Will there be an effect on these three countries? Yes,” she says. “Probably more around the sectors and economies that have some effect on the border countries.”

The real risk, which is more of a long-term issue, is if the United States becomes more isolationist and lets China dictate the terms of global trade. “China is stepping into the void left by the U.S., and it’s ratcheting up its efforts to write trade deals with other countries,” says Kim Catechis, head of global emerging markets for Edinburgh-based investment firm Martin Currie.

At the same time, this could lead Beijing to severely contain American corporate interests in China, if not close off the market altogether. Many of America’s biggest brands have considerable investment footprints in China, such as Nike, Walmart and Apple. This could hurt investors.

Speaking of China, the world’s second largest economy is becoming a more dominant global force by the day. In October, at China’s 19th National Congress, President Xi Jingping was written into his party’s constitution, which has led many experts to believe he won’t step down after his second five-year term. “I believe he’s going to be here for the next 20 or 25 years,” says Catechis.

In some ways, that could stabilize global markets, says Catechis, as Xi Jingping has said he wants to improve environmental conditions, offer better health care and create a more balanced economy. “The country has lifted 400 million people out of poverty, but now it can focus on more pressing things, like clear water and clean air,” he says.

It’s also engaging in more partnerships with other countries, including Pakistan, where it’s building high-speed rail links and power generators, while its massive “One Belt One Road” initiative will create rail and shipping links between China, Europe, Russia and other nearby countries.

This is a longer-term change in the global order, and what it means for investors is yet to be determined, but if America does take a more isolationist past, China will be there to fill the void. “Economically, China is a force to be reckoned with,” says Catechis.

Unrest in the Middle East is always concerning for investors, especially ones who pay attention to the price of oil. While the recent protests in Iran will likely be contained to that region, if things flare up further, and if it does disrupt oil production — the country produces about 4.4 million barrels of oil per day — then we could see energy prices spike, says Hormozi.

If oil rises too quickly — West Texas Intermediate crude has climbed by about 6 percent since the protests began on Dec. 28 — then that could have a negative impact on the global economy. It would push fuel prices higher, which would then make a variety of products more expensive. “If you suddenly don’t have as much oil as you need, then that could create inflationary pressures and become a concern from a GDP standpoint,” she says.

Saying that, she does think regime change in the country would, over the long term, be a good thing. “What’s taking place in Iran could be quite positive,” she says. “If the people can get a more democratic regime and have Iran being a friendlier presence in the Middle East, then that’s good from an economic and geopolitical perspective.”

The World Bank expects the U.S. economy to grow at 2.2 percent in 2018, while many firms, like Goldman Sachs, expect equities to continue climbing, but that could change if there’s a blowup in Washington.

With Donald Trump‘s erratic and often offensive behavior, an ongoing special counsel investigation and an increasingly divided American public, domestic issues could get in the way of a continued bull market.

Nothing has derailed equities so far, with stock markets hitting 26,000 on Tuesday and stocks hitting all-time valuation highs — the S&P 500’s price-to-earnings ratio is around 24 times.

However, if significant information from, say, the Mueller investigation comes out or Trump sends a particularity egregious Tweet, then stocks could turn quickly, says Tony Natale, vice president and manager of strategic research at Bryn Mawr Trust, Pennsylvania-based financial firm.

“The amount of complacency we saw in 2017 was pretty amazing,” he says. “So if there’s some perception that one of the risks comes to fruition, given how truncated the volatility has been, we could see a giant sell-off.”

If the U.S. market does react to a domestic issue, then that could spread to global stocks. “There’s an old saying, when the U.S. sneezes, the rest of the world catches a cold,” he says. “If something unexpected happens to us, then we could see a downturn elsewhere.”

— By Bryan Borzykowski, special to CNBC.com