Who traveled the “middle passage”

Enslaved Africans

Explanation:

Enslaved Africans were traded for raw materials which are returned to Europe to complete the "Triangular Trade" Commercial goods from Europe were shipped to Africa for sale and traded for enslaved Africans. Africans were in turn brought to the regions depicted in blue, in what became known as the "Middle Passage".

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.