The correct interpretation of how the bar graph reflects the information General Grant used to develop his total war strategy against the South is:
The number of soldiers from the North who served was high, so Grant knew he could stand to lose soldiers and still be successful.
Grant's total war strategy involved inflicting significant casualties on the enemy while leveraging the North's larger population and resources. Understanding that he could afford higher losses due to the North's larger pool of available soldiers would inform his willingness to adopt aggressive tactics that characterized his military approach during the Civil War.