What was the Domino Effect?

Domino theory, also called domino effect, theory adopted in U.S. foreign policy after World War II according to which the “fall” of a noncommunist state to communism would precipitate the fall of noncommunist governments in neighbouring states. The theory was first proposed by Pres. Harry S.

Explanation:

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.

answer; ///i do believe that the correct answer is (b) ///middle colony