I was taught as a young man that there were three holidays to explicitly honor the Military and its contributions to freedom. I have no sources and no proof that this is correct. But, it makes sense to me and I hope it will to you as well (BTW, if I am factually wrong, feel free to point it out).
The first is Armed Forces Day. It is celebrated to thank the contributions of everyone who has ever served in the Military whether in peace or war. It doesn't matter if they served three years or 30. Just the fact that they served is enough.
Next on the list was Veterans Day. This was to celebrate the sacrifices and accomplishments of our military men and women who served in time of war. Not much more to say there.
Today is Memorial Day. To a lot of folks it is just another day off of work or a really good shopping day. To some (notably recent HS graduates) it marks the beginning of "adult" life. To others it marks the beginning of the official summer time BBQ and bikini season. Then, to a relatively small group of Americans, it is a day mixed with sadness and pride or even anger.
To me it is the latter. I have lost friends over the course of my time in the Marine Corps. Some died in Beirut in 1983. They will be 19 forever.
Then, there are friends who died on active duty in training accidents, car wrecks, cancer etc. Their loss is no less tragic. I also know Marines killed in the wars and rumors of war that spanned the 1980s through and post 9/11. So today is for the memory of all of them.