The US government saw and treated him as a domestic terrorist and Russian/communist agent. The NY TImes and mainstream media famously attacked him and he was hated by 75% of Americans.
The NSA illegally spied on him and other alleged domestic terrorists:
https://news.ycombinator.com/item?id=29968101
https://www.theguardian.com/world/2013/sep/26/nsa-surveillan...
https://www.smithsonianmag.com/history/why-martin-luther-kin...
He famously called the US government "the greatest purveyor of violence in the world today."
https://www.theguardian.com/commentisfree/2013/jan/21/king-o...
https://theintercept.com/2018/01/15/martin-luther-king-jr-ml...
https://www.history.com/news/martin-luther-king-jr-fbi-j-edg...
https://www.vox.com/2016/1/18/10777146/mlk-day-martin-luther...