Stop in Riyadh begins nine-day trip to Middle East and Europe, as controversies swirl at home.

A welcome by the Saudi royal family and a $110 billion package of new arms deals defined the first day of U.S. President Donald Trump’s maiden trip overseas and sent a message about countering Iran, a shared adversary in the Middle East. Mr. Trump and King Salman bin Abdulaziz Al Saud of Saudi Arabia oversaw the signing ceremony for the agreements just hours after Iranian President Hassan Rouhani won re-election. Mr. Trump’s visit to Riyadh—where large portraits of the U.S. president dotted the city and he swayed to an Arabian dance while encircled by sword-wielding Saudis—is intended to cement an alliance that can serve a counterweight to Iran.

“That was a tremendous day,” Mr. Trump told reporters as he met with Saudi Crown Prince Mohammed bin Nayef. The closer ties between the U.S., Saudi Arabia and other Gulf states includes a new commitment to $350 billion more in defense cooperation over 10 years. It comes at a time when Saudi Arabia is increasingly worried about Iran’s military involvement in Syria and accuses Tehran of supporting rebels in neighboring Yemen—a charge Iran has denied. “The package of defense equipment and services supports the long term security of Saudi Arabia and the entire Gulf region in particular in the face of malign Iranian influence and Iranian-related threats, which exists on Saudi Arabia’s borders on all sides,” U.S. Secretary of State Rex Tillerson told reporters. Saudi Foreign Minister Adel bin Ahmed al-Jubeir said Mr. Trump and King Salman agreed during their meeting that “action has to be taken in order to ensure that Iran does not continue with its aggressive policies in the region.” Saturday’s agreements were peppered between a flurry of fanfare welcoming Mr. Trump at his first stop on a nine-day trip to the Middle East and Europe.

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