The statement that fits all the criteria provided is The Emancipation Proclamation.
- It encouraged African Americans to fight for the Union by allowing them to enlist in the Union Army.
- It strengthened the Union militarily by adding freed African American soldiers to the ranks.
- It shifted the focus of the war to freedom for all by proclaiming the freedom of slaves in the Confederate states.
Therefore, the correct response is The Emancipation Proclamation.