The USA has many allies in the world. Many are natural due to common language or culture between the countries (such as United Kingdom and Canada). These allies have deep relationships that extend beyond military ties between the governments. The connections extend to the populations where there are natural flows of business and tourism. The relationships extend to the founding of the countries.
Other American allies developed over time for a number of reasons. A country may have discovered valuable natural resources (such as oil) or the geographical location of the country may have grown in significance because of evolving military dynamics. Other than such practical (sometimes temporary) reasons, the countries may share little in common. Saudi Arabia is such an example.
The Kingdom of Saudi Arabia has one of the most repressive governments in the world. Minorities have virtually no rights and women have few freedoms. Still, the US government chooses to ignore Saudi policies and distrust between the populations, and focuses narrowly on Saudi oil and military cooperation between the countries. US President Obama underscored the point again on September 10, 2014, with an announcement of strategic military cooperation.
On the 13th anniversary of the attacks of 9/11/01, it is worth remembering that 15 of the 19 hijackers were from Saudi Arabia. Countries with few common values will always remain tenuous friends.
A political music video (music by The Cars):