Mike, first, just a small language matter:"Hannover" is simply German for "Hanover", just like "Deutschland" is German for "Germany".So you're actually referring to HANOVER.
You have to be aware that just like the U.S., Germany, too, has always been made up of STATES.These people were from what was until 1866 the German state of HANOVER (in German: Hannover), the capital of which was the city of HANOVER (in German: Hannover).Just like Pennsylvania, for example, is a U.S. state, Hanover was a German state.When talking about Hanover, you're talking about a state covering an area about the same as that covered by the U.S. states of Maryland and Delaware combined.
You are thus not going to be able to proceed until you do additional research in the U.S. and find out which city, town, or village in Hanover these people were from.
As did most of the major German states, Hanover sided with Austria against the German state of PRUSSIA (in German: Preussen) in the Austro-Prussian War, or Seven Weeks War, of 1866.Austria and her allies were defeated.Prussia thereupon annexed Hanover, which then became what was until 1945 to remain the Prussian province of Hanover.
Following World War II and the break-up of the vast state of Prussia by the Allies, the Prussian province of Hanover, the state of Oldenburg, and the two very small states of Brunswick (in German: Braunschweig) and Schaumburg-Lippe combined to form today's new postwar German state of LOWER SAXONY (in German: Niedersachsen), with the city of HANOVER (in German: Hannover) as its capital.So the former Hanover is one of the four components of today's state of Lower Saxony.
Here is the link to a map of pre-1945 Hanover so that you know what it looked like, Hanover shown in the purplish color.As mentioned above, Hanover covered an area about the same as that covered by the U.S. states of Maryland and Delaware combined: