I am currently writing my MRP on how geography impacted the perpetrator movement of the Rwandan genocide. Other than the frustrating part of finding demographic info from before 1994, I've noticed in my readings that historians (unless military) tend to leave out the impact of geography and terrain in their arguments. I wouldn't call myself a military history by any means but I'm curious as to why this is. I don't think we can divorce history and geography.
I don't think it's fair to generalise that historians "don't" use geography.
An entire school of history, the Annales, emphasised the importance of geography to understanding the longue durée of history. La Roy Ladurie's Montaillou is replete with geographical detail. Similarly, the geopolitics of the 19th/20th century, such as Alfred Thayer Mahan's The Influence of Sea Power on World History and the German Geopolitik school tied geographical circumstance to historical development. Some particular areas are more prone to incorporate geography, such as the American West: Frederick Jackson Turner's The Significance of the Frontier in American History, Walter Prescott Webb's The Great Frontier. A more recent popular example of history incorporating geography would be Timothy Snyder's Bloodlands, where confining his thesis to a specific area of Eastern Europe is central to the argument.
Have a look at landscape archaeology as this may fit the bill. Although I appreciate that it is not technically 'history', it is an example of archaeologists/historians looking at the geography of an area and assessing it as a whole rather than focusing on particular sub-units within that area.
I do agree with /u/EyeStache though, you should define what you mean bu "use". Do you suggest historians assess the effect of geography on history? Or more simply use it to a greater extent as a illustrating factor?
It may also be the case that historians do not often get a chance to get out into the field and consider the spatial relationships between the objects/events that they are studying. This is not to say that historians stay locked in libraries all day, but more that it may not be part of the accepted/budgeted methodology or simply be impossible due to the subject matter.
Environmental history makes extensive use of geography.
How would you propose using geography in a social history, as distinct from a military one?
At least in regards to Eastern Europe, geography is frequently cited as a source for what has happened there. The rise and sudden decline of the Poland and the Polish-Lithuanian Commonwealth have been partially attributed to the lack of natural boundaries, and is a major factor in the reason why Ukraine has not had a Ukrainian state in 800 years: with the open steppe stretching to Mongolia, it allowed any invader to simply move right into the region effectively unopposed. The same can be said for Russia's traditional mentality, especially seen during the Napoleonic Wars and the Second World War: the enemy can move into the west all they want, but they can't outrun the winter snows and spring rains and floods.
I don't know if that's what you mean, but geography is definitely recognised when dealing with that part of the world.
Jared Diamond's Guns, Germs, and Steel (while really popular, rather than academic, history) is heavy on the environmental determinism school of thought. It does exist as a concept, though. For example, the classic history of the Dust Bowl relies on retrospective weather analysis to explain why people believed that "rain follow[ed] the plow."