Donald Simpson's study of the black communities in Upper Canada before 1867 is a valuable contribution to our understanding of how the Underground Railroad (UGRR) undermined slavery in the US. Based on detailed research, he examines what happened to fugitive slaves and free blacks who fled to Canada, especially after the Fugitive Slave Act of 1850. Many of them returned to the US to fight in the Civil War, demonstrating their commitment to freedom and justice for all.