In Lincoln's era, the Republican Party was newly formed by anti-slavery Democrats, Free-Soilers, and Whigs, which dissolved as a party in the 1850s. Their main concern at this time was the abolition of slavery. After that was achieved with the Emancipation Proclamation in 1863, the Republicans focused on Reconstruction, but quickly ended this project with their concession to the South in the form of the Compromise of 1877, signed by Republican President Rutherford B. Hayes.

Until the 1930s, most blacks either did not vote (black men did not gain the right until the Fifteenth Amendment was ratified in 1870; black women did not gain the right of suffrage until 1920) or tended to vote Republican, due to the party's association with abolition. Of course, voter intimidation was very common in the South, which was a stronghold for the Democratic Party. This affiliation persisted, even after the sweeping reforms created by the New Deal. Republicans, however, were opposed to Roosevelt's economic plan.

By this time, the Republican Party became the favored party among those in the West, of wealthy people, and of those who lived in the growing suburbs. Most importantly, Republicans were overwhelmingly white Anglo-Saxon Protestants. Meanwhile, urban areas became more heavily Democratic. This shift coincided with the migration of blacks to Northern cities at the beginning of the twentieth century, as well as the influx of immigrants from Southern and Eastern Europe and Asia. These new citizens, particularly blacks, relied on Franklin D. Roosevelt's reforms, even though, arguably, they were not most directly intended for these groups.

The realignment in the Republican Party in the 1930s -- from a party formed to address a social injustice to a party that became increasingly anti-immigrant and staunchly anti-union -- is directly related to Roosevelt's policies and to changes in demographics. The Republican Party's association with white Anglo-Saxon Protestant citizens has persisted to date with few exceptions.

This is not to say that Democrats were more enlightened. During the Civil Rights era, many Southern Democrats, known as "Dixiecrats," were firmly opposed to advancements for blacks. Meanwhile, some Republicans, like former New York governor (and, later, Vice President) Nelson Rockefeller, made great strides against discrimination towards blacks and women in areas such as housing and education. However, Rockefeller was a moderate Republican serving from the mid- to late-1960s, a considerably progressive era, due to Lyndon B. Johnson's leadership. 

Under Johnson, the Civil Rights Act of 1964 was signed, followed by the Voting Rights Act of 1965. Johnson famously said that, with the stroke of his pen, the Democratic Party, to which he belonged, would lose the South forever. His premonition came true. The South, with the exception of West Virginia, became firmly Republican. The spiteful exit of the South from the Democratic Party (though, today, a couple of states have returned and others may soon return) forced a shift in values in the Republican Party. While the party retained its anti-labor platform and its distaste for higher taxes on the wealthy, it also absorbed a more socially conservative strain, drawn from Fundamentalist values that are more intrinsic to the South and parts of the Midwest.

These values became centralized in the Republican Party with the election of Ronald Reagan in 1980. The social values platform on which Republicans claimed to stand remains pertinent to them today. Platforms related to the rights of immigrants, blacks, and women, which began to be addressed in the 1930s, remain more closely associated with the Democrats -- the pro-slavery party of Lincoln's time.

The present day Republican Party is very different from the party of Abraham Lincoln as its core ideology has undergone radical change. The party was founded on the principle of opposition to the expansion of slavery. This was in reaction to the Kansas-Nebraska Act, which was designed to open up the Kansas and Nebraska territories to slavery. This would have gone against the Missouri Compromise, which forbade slavery north of 36°30'. During the Lincoln era, the Party stood for the abolition of slavery and high tariffs to protect American industry; it introduced the income tax and generally favored big government. The party was dominated by moderate Protestants from the Northern states, African Americans, and owners of big businesses. Later on, the party also had an expansive foreign policy under William McKinley and Theodore Roosevelt. The Republicans dominated government between the Lincoln era and 1932, when Franklin D. Roosevelt came to power under the Democratic Party. The Republicans opposed the New Deal and this led to their defeat in most states in the country. This began the process of the changes in the Republican Party as it shifted from the party of big government to the party that wanted limited government. The party, however, advocated for African American rights and pushed hard for the Civil Rights Act in 1965. However, once the Democrats also accepted the idea of Civil Rights, the Republicans started to court the Southerners who opposed desegregation. The party thus began losing support in the more liberal North and amongst African Americans as it expanded in the South, where many abandoned the Democratic Party as it became more liberal. This process accelerated under Ronald Regan. Most Republicans admire Reagan mainly because he set the foundation of the present day Republican Party and completed the transformation that began after the Republican defeat by Roosevelt. Reagan consolidated the Conservative voter base by bringing together evangelicals and conservative Catholics to form the ‘moral majority’ by supporting various conservative issues such as opposing abortion. He established the Republican ideology of supporting low taxes and reducing government spending. He also had an aggressive foreign policy against the USSR and increased military spending. Since Reagan’s era, small government, low tax rates, focus on national security, opposition to large scale immigration, and appealing to a mainly white suburban voter base have been part of the core ideology of the Republican party until the rise of Donald Trump in 2016.