Final answer:
Lee responds to the suggestion that the war cannot be won by ultimately surrendering to Union forces, acknowledging their superior numbers and resources.
Step-by-step explanation:
When Longstreet suggests to General Robert E. Lee that the war cannot be won, Lee ultimately responds by accepting the reality of the situation and making the difficult decision to surrender. Observing the dire circumstances his troops were enduring and the overwhelming numbers and resources of the Union forces led by General Ulysses S. Grant, Lee found continuing the conflict to be futile and beyond his endurance.
This acknowledgment led to the exchange of letters between Lee and Grant, culminating in their historical meeting at the McLean house in Appomattox Courthouse, Virginia, where Lee surrendered the Army of Northern Virginia on April 9. In his final address to his troops, Lee highlighted that their defeat was due to the sheer scale of opposition they faced, rather than any internal weaknesses, stating that they had been "compelled to yield to overwhelming numbers and resources."