Final answer:
The Civil War dramatically shifted the balance of power towards the national government, with the Union's victory affirming federal supremacy and the imposition of conditions for readmitting Confederate states into the Union, including ratification of amendments. The Emancipation Proclamation and extensive government mobilization efforts also significantly altered federal politics.
Step-by-step explanation:
Impact of the Civil War on Federal Politics
The event that impacted federal politics to the greatest extent during the Civil War era was the profound shift in the balance of power towards the national government. This shift was a consequence of the Union's victory which confirmed the federal government's dominance over the states and effectively ended any legitimate claims for state secession. Further cementing this shift was the imposition of conditions for the readmission of former Confederate states to the Union, like the ratification of the Fourteenth and Fifteenth Amendments. Additionally, the Emancipation Proclamation of 1863 which freed all enslaved people in the rebellious states, and the mobilization of resources by the federal government during the war played crucial roles in altering the political landscape. These actions represented a significant increase in government activism and a growing interconnection between the government and everyday lives of citizens.