The United States Congress, in the years leading up to the Civil War, was a virtual battleground in which Democratic Southerners and mainly Republican Northerners would bully each other as often as debate. Threats, fistfights, and the carrying of weapons were common. People elected representatives to Congress partially based on their confrontational ability. This attitude, in which compromise was seen as a sign of weakness, made it very difficult to agree on specific items of legislation.

All this changed when Southern states began to secede from the Union and their representatives withdrew from Congress. Just before secession, in 1860, there were 234 representatives and sixty-six senators in Washington. The Democrats held a Senate majority, and the Republicans had a majority in the House of Representatives. However, after secession, in the beginning of 1863, there were only 180 representatives and fifty senators, and Republicans held comfortable majorities in both the Senate and the House of Representatives.

This enabled Republicans during the Civil War and Reconstruction to pass several pieces of legislation without significant opposition. For instance, to help finance the war, they passed the Legal Tender Act of 1862, which authorized the production of paper money. The Homestead Act of 1862 opened up millions of acres of public land to US citizens. The Morrill Land Grant Act enabled the creation of colleges with funds from federal sales of land. The Pacific Railroad Act authorized and promoted the construction of a transcontinental railroad. Republicans also initiated a national income tax with the Revenue Act of 1861. Although not all of these pieces of legislation had a direct bearing on the war, they were all part of the Republican platform and were able to pass due to the absence of Democratic opposition.

During the Civil War, Congress was also able to implement several pieces of legislation that hastened the ultimate abolition of slavery. In 1862, Congress ended slavery in the District of Columbia. It also ordered the army not to enforce the Fugitive Slave Act, which meant that slaves fleeing their Southern owners did not have to be returned. Congress enabled the creation of a Freedman's Bureau to assist former slaves from the South with clothing, supplies, and shelter. After the war, Congress was able to pass the thirteenth amendment to the Constitution, which abolished slavery in the United States.

The absence of Southern politicians from the House of Representatives and Senate—and the fate of such elected officials was handled on an ad hoc basis given the unique nature of the situation—allowed Northern elected officials to pass major legislation that ignored the wishes and conditions of Southern states. How to resolve the matter of Southern legislators voluntarily leaving Congress to assume positions in the Confederacy and the matter of Southerners remaining in Congress proved understandably vexing. Some Southern congressmen and senators were expelled. Some Northern officials favored treating the seats of those departed for the South as vacant. Others supported the elimination of those seats, consistent with the Southern states’s movement toward secession. With the formalization of secession, the fate of such elected officials became largely moot. Congress became a Northern institution reflecting those states’s priorities and interests.

Among the most far-reaching and consequential actions by the Civil War-era Congress was passage of the Homestead Act, a law that allowed individuals and families to settle plots of public land at no cost under the condition that these settlers would develop the land. With the delegitimization (in the eyes of the North) of the South’s legal standing, and with the South’s heavy dependence on the agricultural industry, the threat to land previously dedicated for agricultural purposes for non-agricultural (e.g., industrial) activities was a serious blow to the Confederacy.

Also of considerable significance to the South following its secession was passage by Congress of the Morrill Tariff Act, which increased tariffs, taxes imposed on foreign goods entering the United States. The North was determined to advance the cause of industrialization with the same fervor evident in the South’s efforts at resisting industrialization and expanding agriculture. Tariffs increase the cost to American consumers/businesses of imports. The South, less prosperous than the North, would suffer greatly with an increased cost for foreign goods. The Act’s passage in 1861 was not a cause of the war—the South’s secession was already a done deal due to differences with the North over slavery—but it marked a major development that might not have occurred had the South not withdrawn its membership from Congress.

The Civil War occurred because of the depth of divisions between North and South, principally over the issue of states’s rights (read: slavery). With the absence of Southern representation in Congress, therefore, Northern legislatures were free to advance a legislative agenda at odds with Southern interests.

The absence of Southern members of Congress allowed the Northern Republicans (and Democrats) to act in the economic interests of the North during the Civil War.  The main impact of this was to allow the Congress to pass laws that helped to develop the west. 

Before the war, the North and South could not agree on developing the west.  Of course, the South wanted slavery to be allowed while the North did not.  This blocked any real agreement on what to do.  With the Southerners out of the way, Congress developed the west.  In 1862, it passed three laws that were very important in this.  It passed the Pacific Railroad Acts, the Homestead Act, and the Morrill Land Grant Act.  These laws helped to build the railroads that brought settlers west.  They helped to lure settlers with the promise of cheap land.  They helped to create colleges that would help develop new and better agricultural techniques.

By doing these things, the Congress was able to help to open the west to white settlement and economic development.