Dow gives investors whiplash after the worst day of the year for stocks

Several negative signs are weighing on markets: The yield curve flashed a recession warning sign Wednesday. The global economy is slowing down. And the trade war, which has unnerved investors for a year and a half, will continue to loom over markets until it is completely resolved.

But Walmart on Thursday suggested American consumers are confident in the economy, and will keep spending throughout the rest of the year. And China tried to ease trade war concerns by saying it remains open to negotiations with the United States.

The push and pull was evident Thursday morning, as Dow futures swung wildly: Up 200 points, down 200 points and up nearly 200 points once again. After the Dow opened up more than 100 points, it turned negative before heading for positive territory once again.

By mid-morning, the Dow was up 20 points. The S&P 500 was 0.3% higher. The Nasdaq, with its many tech companies, was flat. Tech companies would be particularly hurt by an escalation of the trade war.

China

A threat from China started Thursday's markets on the wrong foot. The Chinese Ministry of Finance said it would "take necessary countermeasures" after the United States earlier this month announced a new 10% tariff on $300 billion in Chinese goods. China said the new tariffs "seriously violated the consensus" that Presidents Donald Trump and Xi Jinping agreed to at the G20 meeting earlier this year.

China has previously said it would retaliate against any new tariffs tit for tat, but the statement nonetheless spooked markets.

Yet China's Foreign Ministry spokeswoman Hua Chunying then calmed investors fears in a press conference Thursday, when she said China remains hopeful the United States and China can "work out a mutually acceptable solution."

None of this is particularly new. China has said all this before. But investors are on edge, turning some trade war molehills into mountains.

Also, more signs of the global economic slowdown emerged Thursday, as China injected $2.4 billion in stimulus into the Hong Kong economy, according to Bloomberg. The Hong Kong protests have hurt the tourism economy. The airport has been shut down after protesters barricaded themselves inside.

Walmart

By contrast, Walmart said its outlook for the rest of 2019 has improved after Americans shopped more at US stores in the second quarter. With its huge network of thousands of stores, Walmart is a barometer for consumer spending.

The company said sales increased 2.8%, and it raised its guidance for the remainder of the year, signaling optimism about the strength of its business. Shares of Walmart, a Dow component, gained close to 5%.

But Cisco, another Dow component, provided a much gloomier outlook. Cisco is a bellwether for the global economy: The networking technology company sells telecommunications equipment around the world, including routers and switches that power cell phone and broadband networks. Despite reporting strong sales last quarter, Cisco warned Wednesday evening that weakness in China and other countries contributed to slumping demand for tech products.

Cisco's stock fell 7% Thursday.

The yield curve

Wednesday, the yield curve between the 10-year and 2-year Treasury bonds inverted. That classic recession signal scared investors.

Although the 2/10 yield curve has reverted, Treasury yields, which move in opposite direction to bond prices, remained lower Thursday. The 30-year yield briefly tumbled below 2% for the first time in history.

Although yield-curve inversions have preceded every recession in the modern era, they do not necessarily portend an imminent recession.

-- CNN's Serenitie Wang and Steven Jiang contributed to this report.