The more you actually research the history, reading the documents themselves rather than relying on historians' spin jobs, you find that the "facts" that everyone has taken for granted are not only untrue, but that they are the opposite of what actually happened. When you see enough of this, then you recognize that conspiracy is not a theory: People in power have always done whatever they pleased and changed the story to whatever they wanted it to be.
Abraham Lincoln is credited with freeing the slaves, but that is inaccurate. The slaves were freed by the 13th amendment to the Constitution. (However, through the 14th amendment, the citizenship of the rest of the populace was degraded and stipulations were added—very tricky). If you actually read the Emancipation Proclamation, you will find that Lincoln expressly and specifically freed only the slaves that were in territories (seceded states) that did not recognize his jurisdiction, and he expressly and specifically did not free any slaves that resided in the Northern states of which he was still considered the Executive power! But what were Americans taught? The Civil War was fought to free the slaves, and Abraham Lincoln freed the slaves through the Emancipation Proclamation.
Mere semantics, you say? It is in the fine print that people are swindled out of their life's work, life savings and lives. Actually, based upon the principles expounded in the Declaration of Independence, Abraham Lincoln's military action against the seceding states was tyranny, and I say this purely on principle and as a descendant of American slaves (lest anyone think I'm a white supremacist).
Great men rarely stand up to the scrutiny of a later age. But that's no reason to whitewash them.