Whether you want to believe that slavery ended in America upon Abraham Lincoln's Emancipation Proclamation of January 1, 1863, or upon the surrender of the Confederacy on April 9, 1865, or perhaps upon the ratification of 13th Amendment in 1865, which abolish slavery and involuntary servitude, one could make a strong argument that slavery or its modern equivalence of never really went away. The problem with the defeat of the Confederacy in 1865 is that the same power structure that created the Confederacy still existed, unbowed and unrepentant despite any loyalty documents that were signed, still owning the same land and still having access to the same poor and disenfranchised black people of the South, and although there were federal laws on the books, Union men in town, it didn't take all that long for things to inexorably slip back to the way that they previously were.
That is to say, of course, technically Southern plantation owners no longer owned slaves, as that was illegal, and perhaps considered impolitic, but just as surely Southern plantation owners adjusted to these circumstances by creating "black codes" and other laws and restrictions on black movement and labor, that were backed by southern justice, southern arms, southern violence, in such a manner that freed blacks were forced into positions of servitude similar to slavery to which the prime beneficiary of this labor was reaped in large part by that southern plantation class, trapping blacks into a system that offered no escape from economic deprivation.
It was not until the aftermath of World War II that the pressure to give the black man a fair place at the table of American bounty became something that began to inexorably increase on the Federal government; yet, while on the one hand, America began to become a more liberal society, there was a conscious recognition that jobs that were both labor intensive as well as historically poor in compensation, such as agricultural in all of its many facets, hospitality, and so forth, needed to be filled by somebody that would be satisfied just to have some sort of foothold in America.
The answer to that labor need came from south of the border, in Mexico, and in Central America, to which whether purposely done or by benign neglect, the powers-to-be made sure to differentiate these people from "real" Americans, by first allowing them to slip across the borders in unprecedented numbers, and further to make sure that these people would not be considered to be citizens, but instead be looked upon as undocumented workers, illegal aliens, or whatever. Further to the point to separate these people from Americans, they made sure to setup the logistics of a language barrier; by making Spanish the de facto recognized second language of America. The brilliance of this decision was that, those that are unable to comprehend English, but instead must rely on Spanish to conduct their day-to-day activities of their communication, place themselves into the inferior position of being both stigmatized by authorities and also exploited by labor, because by their language, there are in essence recognized as people that have no rights that need be respected. This means, in effect, that they are subject to "Mexican codes" to keep them in their place, that a "good" Mexican is a Mexican that keeps their head down, does their work well, doesn't complain about working conditions or pay, and should be grateful for the bones thrown their way.
While one could argue that it isn't really slavery when you aren't forced to or compelled to move your feet into America, which while technically true, misses the point that the deliberate exploitation of any human labor, that is further not accorded full civil and economic rights, is a civil crime against humanity and a disgrace to anyone that pledges allegiance to this mighty flag and what it represents.