Nowadays whiskey is usually around 40%, vodka is around 40% and many others spirits seem to be hovering around 35-40%. I remember reading somewhere that beer or some equivalent of beer used to be a much lesser alcohol percentage in the far past than it is today at around 5% alcohol. I am wondering if something similar is true liquors in the American frontier when there was far less regulation, or in that same time period in other parts of America and the world.
Poblehvkin's "a history of vodka" is a pretty good read for the history of spirits. I dont want to just go off memory, so I'll give you a rundown in probably a couple hours when I finish a paper with pretty much the history of vodka and Eastern European spirits including a form of mead and honey based beer. poblehvkin was one of the few to actually go in depth into the history of vodka and considered a top notch secondary source to this day on Russian alcoholic beverages.
This is not a historical answer, but still relevant. Alcohol in alcoholic beverages is produced by the conversion of sugar into alcohol and carbon dioxide by yeast. Yeast only works up to a certain percentage (approximately 12% - 15%). Wine is between 12 and 15% for that reason. Beer is lower since they let it ferment for a shorter amount of time. Hard liquors get the higher percentage through distillation, making the percentage higher. I believe that if you distill something three times, you will get around 40% (hence triple distilled vodka). I do not know when these distillation techniques and practices started becoming common though. Lastly, a small historical comment: Beer and wine were consumed in a little bit of a different way than they are consumed now. In roman times wine was usually diluted a lot, same as for beer in Medieval times.