When talking about the Ku Klux Klan (better known as the KKK), we need to distinguish between two versions of it. The KKK was strong in the South during the Reconstruction era. It was strong again, but not only in the South, in the 1920s. To truly talk about the KKK, we must discuss these eras separately.
In its original incarnation, the KKK was founded in 1866. The main goal of the organization at that time was to resist Reconstruction. In order to do this, it tried to intimidate people who supported the Reconstruction governments in the South. It did this largely through violence. Many of the people whom it intimidated were African Americans and the Klan was a white supremacist organization.
After Reconstruction, the KKK largely lost its purpose in the South. However, when the 1920s came around, it returned to prominence. This time, it was less of an anti-black organization and more of an anti-immigrant and anti-modernity organization. The new KKK was in favor of “100% Americanism.” It felt that traditional American values were being degraded by the new immigrants. It was especially opposed to Catholics and Jews. It also hated the new morality that gave rise to such things as the flappers. The KKK was strongly in favor of Prohibition. It was still white supremacist, but it was more concerned with opposing immigrants and people who did not hold the same traditional values as the KKK.
Thus, the KKK has had two different incarnations. First, it was an anti-black and anti-Reconstruction organization. Later, it was more concerned with preserving what it saw as Americanism and with fighting the influence of immigrants and modernity.
Your question implies that the Ku Klux Klan (KKK) is no longer in existence; though it has undergone several changes over the years, the KKK still exists in America.
The Ku Klux Klan was established in the South in the first few years after the Civil War (between 1866-1870) as an organized protest against the reforms imposed by the Republican Party to give blacks voting and economic rights. The founders were a small group of Confederate soldiers, and the founding beliefs included white supremacy and white nationalism (anti-immigration).
The group used violence and intimidation against the leaders of the Republican Party, both whites and blacks. To conceal their identities, they wore white robes and masks when they gathered in an attempt to intimidate and terrify. Congress tried to restrict the racist organization with what is known as the Force Acts; while the laws were not completely successful, KKK activity receded for a time in the early 1870s; however, the group's efforts resulted in a sweeping majority of white, Democrat segregationists gaining political power across the South.
A resurgence of the KKK began in Atlanta in the 1920s with somewhat more political objectives than the earlier group. The organization was particularly violent in the South but permeated the rest of the country, as well. Cross burning became a hallmark of this group. This time the KKK especially promoted white nationalism and increased attention to the dangers of alcohol and the Catholic church. By the 1940s, the KKK again diminished, though it surged again after World War II.
In the 1950s and '60s, the KKK in the South was adamantly opposed to the Civil Rights movement and desegregation in the South, and violence erupted again.
Today there are still chapters of the KKK in America, though the number of members is purported to be fairly small. The KKK is designated a hate group by some organizations and is still known for its white supremacist, white nationalist, pro-Christianity, anti-Communist beliefs.
The headline on the top of the KKK website, however, paints a different picture. It says:
Bringing a Message of Hope and Deliverance to White Christian America! A Message of Love NOT Hate!
The organization claims to seek non-violent resolutions to the issues it promotes, which include renewing Christian principles in America. Despite this current claim, the KKK over time is known for its racist violence perpetrated by whites against blacks.