The police have ever been henchmen of the capitalist class that has ever ruled this country. Their core purpose is to protect the capitalists’ private property—historically including chattel slaves—and to discipline labor.

Now that we’ve reached imperialism, the monopoly stage of capitalism, the police are brutalizing anyone who stands between the capitalists and their imperial interests, in this case their interests in West Asia.

https://en.wikipedia.org/wiki/Police_brutality#History

Early records suggest that labor strikes were the first large-scale incidents of police brutality in the United States, including events like the Great Railroad Strike of 1877, the Pullman Strike of 1894, the 1912 Lawrence textile strike, the Ludlow massacre of 1914, the Great Steel Strike of 1919, and the Hanapepe massacre of 1924.

The racist roots of American policing: From slave patrols to traffic stops

TL;DR: ACAB