Alternative History settings essentially ask "What If?". They investigate what might have happened if history had taken an alternative path, presenting different outcomes. Many Alternative History settings involve Sci-Fi elements such as Time Travel.
This list takes a relatively 'strict' interpretation of Alternative History settings. It specifically only includes settings where there has been a specific societal drift, societal change. That is to say that a show that happens to be set in a historical or contemporary era but has magic does not apply to this. There has to be specific political, social and/or religious differences between the settings to count on this list.