The Resurrection of the KKK

In the 1920's, the KKK became prominent again. However, although they had the same goals to preserve the "purity" of WASPs (White Anglo Saxon Protestants) of America, this time the KKK had different plans and ways to achieve this goal. The Ku Klux Klan was formed in 1866 and had members from just about every southern state by 1870 (according to history.com). During this time, the KKK used terror in the form of bombings (they bombed black schools and churches), as well as lynchings (black men and some white activists were brutally killed and displayed). Fast forward to the 1920's, and now the KKK are lashing out against Mexicans, Asians, white Jews and Catholics, and other non Protestant groups. This time, the methods of terror used by the KKK included riots and other public displays, lynching, burning the cross, and abduction. In the 1920's, the resurgence of the KKK was caused by the rise in immigration numbers, the increased movement of African Americans, and industrialization/urbanization, and as a result, the number of participants actually ended up reaching 4 million members, but the population ended up falling drastically within 8 years. So, why did the population end up falling so much in the late 1920's, and why did it become so popular in the first place? Also, what happened to former members who left the group?