In the early republic, Congress was a colorful, exciting, unpredictable, and contentious branch of the United States government. The members constantly quarreled but often deliberated and compromised through persuasive oratory and rational conversation. Congress was divided by party and sectionalism, but was guided through these difficulties by legislative statesmen. The Congress continued to function as the undisputed law making body of the people of the United  States. Even during some of its most tumultuous years, from 1789 until the outbreak of the Civil War in 1860, the Congress effectively governed the nation.

With the defeat of the Confederate States of America in 1865, the victorious Union faced the question of how to rebuild a single nation. Congress and the Democratic Party were tainted by their association with “Copperheads,” who had sought peace at the price of recognizing the Confederacy as a sovereign nation. For this reason, the powers of both Congress and the Democratic Party were at their lowest point, and the Republicans and their president reigned supreme. After President Abraham Lincoln’s assassination, the new president, Andrew Johnson, controversially attempted to allow the former Confederate States’ representatives to take their seats in Congress. This move outraged the populace of the North and West. Not only were former Confederate rebels returning to the Congress, but these states would have even greater representation and power, as the passage of the Thirteenth Amendment allowed the Southern states to count their massive African American populations in full for the first time in their history.

As the United States entered a new century, it found itself a new country. Reborn from the ashes of the Civil War, the nation was establishing itself as a world economic power. The promise of freedom and opportunity had brought millions of European immigrants to the United States, and more were coming. These sweeping changes led many progressive reformers to advocate change at the state and national level. The Congress of the United States, too, was swept up in the spirit of reform. Constitutional amendments passed during this era fundamentally altered how the Congress functions. In addition, Congress changed its rules to reduce the influence of party leadership and decentralize power, distributing it to individual members and committees. As the century progressed, the legislature continued to shift and adapt to better respond to its ever-expanding reach.