If you look at that timeline again, you'll see why some people are freaking out. White America (not exclusively but predominantly) has had the power since the founding of this country. Over the last few decades, they've been forced to share more and more of that power and influence over culture, economics, and politics.
Human groups fight when there is scarcity. In the past, when we were hunter gatherers, humans dealt with scarcity with brief skirmishes before one side more or less agreed to GTFO and move to a different pond, or beach, hunting ground or island. That probably explains why humans migrated of Africa in the first place; it was a means of conflict resolution.
Civilization changed all of that. It created land - land that people owned. It also created much larger populations that had to be sustained somehow. We needed specialization, people with specialized knowledge and skills. This transformation to sedentism and population growth tied people to territory, and it made land worth fighting over. It created resource scarcity, but it also created political and cultural scarcity as well. Civilization led to inequality, with different classes of people ranked according to various criteria. Ever since, people have not only fought over the hard resources such as land, food, water, shelter, etc, but also over their standing and who gets to control the population.
And that's exactly what's happening now in the U.S. Mostly white, Christian, conservative America sees its power slipping away. It cannot halt or reverse this trend at the ballot box because they are increasingly outnumbered. This is why the big lie is so important -- they need some sort of 'story' to tell that lays out the case for what they are doing since they cannot just come out and say 'Look, **** you guys, we're done with democracy as we know it.' Mind you, it's not a rational or logic or fact-based case -- that's not the point at all. It's a story, a legend, a tale that is told to ultimately explain why they must do what they intend to do, which is to take control of the country for their 'kind' however they see fit.