Because of the British victories at Brandywine and Germantown, George Washington and the Continental Army were forced to spend the winter of 1777-1778 at

Valley Forge

Explanation:

With the onset of the bitter winter cold, the Continental Army under General George Washington, still in the field, enters its winter camp at Valley Forge, 22 miles from British-occupied Philadelphia.

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.