According to the US Census Bureau Arab Americans trace their ancestry to the western Asian countries of Lebanon, occupied Palestine, Syria, Jordan, Iraq, Bahrain, Qatar, Oman, Saudi Arabia, Kuwait, United Arab Emirates, and Yemen, the northern African countries of Morocco, Tunisia, Algeria, Libya, Sudan, and Egypt. Lineage is traced via Arabic languages, not according to "race" or religion.
The earliest Arabian immigrants to the US are considered to have arrived in the mid-nineteenth century from Syria and Lebanon. According to American Demographics, a Dow Jones publication, These earliest Arabian immigrants espoused a Christian faith and commonly established themselves as merchants.
Arab immigration to the United States was curbed from 1925 until 1948. During this period that was experiencing the effects of two "World Wars" US immigration policies favored immigration from European countries.
According to Yogi Cole of Diversity, Inc., "Since World War II, the predominant Arab immigrant has been a person from the capitalist class, the landed gentry, or an influential urban family fleeing from a country that suffered political upheaval... Arab Americans are predominantly Christian... It was only in the 1980s, that the Muslims started their immigration. Muslims were mostly city dwellers' as opposed to the Christian farmers of earlier immigration."
Census 2000 in the US reports that about ".2 million people in the United States reported an Arab ancestry... up from 860,000 in 1990 and 610,000 in 1980... The population of Arab ancestry increased 41 percent in the 1980s and 38 percent in the 1990s." 
Polls by advocacy groups estimate the population of Arab Americans to be twice the Census count: between 2.5 million to 3 million.  (It should be noted that claims as to an ethnic or racial ancestry on the Census are voluntary by nature. In this category of the US Census "no response" is a frequent response.)
Sources & External Links
- U.S. Census Bureau, Press Release, Report on Arab Population, December 3, 2003