The Black Rider - Valley of Smoke. The Black Rider Series, #3

The Black Rider - Tom O'Leary - expert in side arms (Colt 1860 Model), rifle (Henry 1860) and stock whip. Black stallion horse - Diamond. Tom is a wanderer of justice - with a dark secret - he is not of this planet. Sent by distant galaxy to examine the people of earth and see if they are worth invading. Hidden away in a new cave is his spaceship, temporary home, with advanced technology. A computer chip in the horses brain allows him to communicate and direct it.
His weapons look like normal cowboy arms of the time, but with the touch of a tiny button can turn into something more. In the previous story he breaks protocol and interferes with the conflicts of the city, but exposes himself and has to leave and return to report his behaviour only to return to observe the American Civil War and once again going beyond his remit.. Now in 1869 after the civil war returns once again to observe life post war.
Meeting some characters that have moved on from war to civilian life. It is revealed that other Riders exist on different continents observing their own areas of the Earth.