For decades, a simple quid-pro-quo formed the basis of US-Saudi relations. Riyadh provided the oil, Washington provided the security.

"It's become infinitely more complicated than that," James B. Smith, the American ambassador to Saudi Arabia from 2009-2013, told DW.

On Friday, US President Barack Obama welcomes Saudi King Salman to Washington for the first time. Salman, 79, ascended the throne last January after his half-brother Abdullah passed away.

When the two leaders meet, President Obama will represent a nation that's become increasingly self-reliant in energy production, while King Salman will represent a nation that's become increasingly self-assertive in its foreign policy.

Last March, Riyadh launched a military intervention in neighboring Yemen after Houthi rebels drove the US-Saudi backed government from power. Though the US has provided intelligence and logistical support, Washington is largely on the sidelines, according to Smith. For the first time, Saudi Arabia is clearly in the driver's seat.

"Traditionally they've operated in the shadows, using money or influence," Smith, now president of C&M International, said of the Saudis. "The Yemen campaign indicates a much more muscular foreign policy. I don't know if this is an aberration or a trend, it's too early to tell."

Quiet diplomacy not enough

A majority Sunni nation, the Saudis see in Yemen an attempt by Shia Iran to encircle them, according to Smith. Both Riyadh and Washington have accused Tehran of supporting the Houthi rebels, who are also affiliated with the Shia branch of Islam.

The Saudis have largely taken matters into their own hands as the United States under President Obama has been hesitant to intervene in the Middle East's many conflicts. According to Fahad Nazer, the Saudis are concerned that the United States has disengaged from the region.

"Given the upheaval, turmoil and violence all around them in the Middle East, they've come to the conclusion that their quiet behind the scenes diplomacy is not enough these days," Nazer, a former political analyst at the Saudi embassy in Washington, told DW.

"There's very wide support in Saudi Arabia for the idea that the Saudis themselves should be the ultimate guarantors of their own security," said Nazer, now an analyst at JTG Inc. "The idea that Saudi Arabia has to depend on the US or any country as the ultimate guarantor of its security is no longer acceptable."

Concerns about Iran deal

President Obama's determination to reach an agreement with Iran on its nuclear program also unsettled the Saudis, who are concerned about Tehran's alleged ambitions not just in Yemen, but in the broader Middle East.

"If you go back six to eight months ago when the Saudis and others expressed great displeasure over the negotiations, it had to do with the issue that they wanted Iran's destabilization strategy and Iran's meddling to be a key issue in the negotiations," Smith said. "That was the issue that was paramount even over the nuclear file."

Now that the negotiations have concluded, the United States has shifted its focus to selling the deal both at home and abroad. Both Secretary of State John Kerry (pictured above with King Salman) and Defense Secretary Ashton Carter have visited Saudi Arabia to reassure the kingdom.

But according to Smith, when King Salman sits down with President Obama, the monarch will want to know what the US is "going to do to get the Iranians to stop interfering in the internal affairs of other countries and destabilizing the region."

Trade and investment

King Salman's visit won't just focus on security issues. According to Smith, the Saudi monarch has also brought a large business delegation with him.

"One of the key issues that this trip is focused on is the business community and investment and the growth of their private sector," Smith said.

According to Nazer, Riyadh has been trying to diversify the Saudi economy and upgrade the country's infrastructure for years.

"They long ago came to the conclusion that their economy was too dependent on crude oil specifically, but petrol products in general," Nazer said.

Saudi Arabia officially opened its stock market to foreign investment in June. Though the US has long had an advantage in developing the all-important oil industry, Riyadh has increasingly sought investment from other countries as it looks beyond petroleum.

"Now the Saudis want Chinese, Japanese, South Korean and European companies to help work on all these different projects to expand and maintain and improve the infrastructure," Nazer said.