An overview of the relationship between the United States and Saudi Arabia over the past century.

Saudi Arabia and the United States have a relationship that stretches back almost a century, since the 1933 kickoff of oil exploration in the kingdom.

Since then, the two countries have maintained a baseline of economic and security cooperation that has kept ties between them strong. Saudi Arabia is the US' largest foreign military sales customer, and the US has long had a physical and advisory military role in the kingdom.

While today there seems to be a strategic alignment between Saudi Arabia's interests in the region and those of the US, mostly centring around controlling Iran's regional reach, there have been low points in this relationship that were brought about by major events. Saudi Arabia has always sought balance between its role as a leader in the Arab world and its strong ties to the US.

During the final years of the Obama administration, "relations had undergone a period of difference of opinion", as stated by a senior advisor to Prince Salman last March. These differences of opinion were largely centred around Saudi Arabia's refusal to engage with Iran and the Obama administration's cautions to the kingdom about the civilian toll of the war in Yemen.

However, under the Trump administration, relations have warmed and the US is fully supporting Saudi Arabia in its regional role.

President Trump had maintained an extremely negative view of Saudi Arabia for years before being sworn in as president, saying that he was "definitely not a big fan" of the kingdom, and that the US should not be working to "support Saudi terrorists".

This position changed, underlined by an extremely cordial visit that that Deputy Crown Prince and Minister of Defence of Saudi Arabia Prince Mohammed bin Salman made to Washington, DC.

In a statement after this meeting, bin Salman's senior advisor's statement touched on the various topics discussed, which included an expansion of economic cooperation, an agreement that Trump's travel ban was justified and was not a "Muslim ban", and the two leaders' agreement on "the same views on the gravity of the Iranian expansionist moves in the region".

OPINION: US-Saudi relations in the Trump era

Trump will be visiting Riyadh on Friday on his first international trip as US president. He will follow that with visits to Israel, the Vatican City, Brussels and Sicily.

During the trip, Trump will be participating in three summits: the first between himself and Saudi King Salman, the second with the leadership of the member states of the Gulf Cooperation Council (GCC), and the third with heads of state and high officials from a number of Arab and Muslim states.

The first Saudi-US summit is expected to focus on cooperation between the two countries on security, economy and regional politics. Saudi Arabia is expected to press the US on Iran and reiterate its position that Iran's activity in the region is the cause of a great deal of instability.

There are high expectations that an arms deal worth $100bn that has been in the works for awhile will be ready by that date. A US official speaking on condition of anonymity told Reuters that the total value of the arms sales could exceed $300bn over the next decade.

The discussion of Iran and its supposed destabilising role in the region will carry through to the second, GCC-US summit, which will focus on "security and stability" in the GCC region and the building of trade ties.

During the third summit, which will include the leaders of a number of Arab and Muslim states, Trump is expected to deliver a speech on the religion of Islam, the US' positive relationship with it, and the distortion of the positive image of Islam by groups who use it for their own violent gains, exhorting the gathered Arab Muslim leaders to fight this distortion in any way they can.

This has been received with a great deal of derision on social media, especially after it was revealed yesterday that the man writing the speech was Stephen Miller, a senior Trump adviser who played a large role in the creation of the travel ban known as the Muslim ban earlier this year.