When I finished my years at the University of Utah for both of my degrees, it turned out that I had more hours of classes on military history than any other subject. I spent the next couple of years on active duty in the Army during the Vietnam War, but ended up serving in Panama rather than going to Vietnam. I bring this up to make a point about genealogy. Genealogy is history, no matter what the attitude of the academic world or anyone else for that matter and if you are doing genealogical research, you ignore history at your peril. I naturally think of the wars because this is my background. But many researchers have ignored military records, even when those records are indicated by the time and place where their ancestors lived.
I first became involved in the military history aspect of genealogy when I tried to determine when and how my Grandfather served in World War I and on the Mexican Border. Even though I had direct knowledge that he served, it took me a considerable amount of research to find the units he served with, but that is another story.
Surprisingly, statistics and some details about wars in America are hard to come by. Many of the casualty figures, including dead and wounded, are estimates rather than accurate numbers. This is particularly true for older conflicts. There is also a problem with the definition of a "war." For example, when my Grandfather LeRoy Parkinson Tanner served on the border with Mexico in about 1916, that military action was not considered a "war" as such and is not usually listed as a war in compilations of casualties.
Wars are important to genealogists because they generate records. Military records can be both surprising in the amount of genealogical data they contain or very disappointing in the lack of information. Records about the involvement of the individual soldiers can be scattered into a variety of record sources.
Someone commented recently to me that I seemed to have a rather dim view of the average person's knowledge of history. I can say that my experience in this regard simply forces me to that attitude. Among genealogists, the number of people who are aware of our history, is likely quite a bit greater than the general population, but there is still a lack of awareness of all of the military conflicts in America, both before and after Independence from England, that could have generated records.
The earliest American war is generally believed to be King Phillip's War from 1675 to 1676. However, there is also the Pequot War of 1637. Since that time, I count more than 30 different conflicts that could be considered to be wars, both declared and undeclared. For example, as I write this post, is there a U.S. war going on? Answer that question and you can see why the number of wars may vary. But the fact of the matter is that millions of Americans have fought in various conflicts from early colonial times to the present and their records have piled up in various repositories around the United States and abroad for hundreds of years.
With regard to King Phillip's War, I find about 5,000 books listed in WorldCat.org on that subject alone. You might want to start with the FamilySearch.org Research Wiki article, Massachusetts Military Records. You might also check out the article Colonial Wars, 1607 to 1763. There are hundreds, if not thousands, of websites dedicated to military history.
The rule here is that if your ancestors lived in America when one of these wars was in progress, there is a possibility that someone in your ancestral family was involved in the war and you may find records about your family that you previously were not aware of. If you think about it you may wish to go to the Research Wiki article, United States Military Records, to get started.
Of course, military records also exist in almost every other country of the world. No matter where you live, you just might try researching the military records for your own country.