Captain America v5 #49
There’s a tendency in comics, and all fiction really, for women in notably male-dominated vocations, ie punching people, to attribute it to male influence. She grew up with four brothers, or her dad wanted a boy, her boyfriend was into it, etc. It’s rare for a female character to just up and do something you usually perceive to do a man’s thing to do.
One reason I like the Carter girls is that Sharon became a SHIELD agent because her aunt and idol was a French Resistance operative. Her aunt. Not her dad, or uncle, or whoever. Her hero and idol is a woman.
Why’d Peggy join the French resistance? Because fuck Nazis, that’s why. She wasn’t involved with a French lover who was killed by the Nazis, her father wasn’t a soldier, she was studying in Paris when the Nazis rolled in, and Peggy Carter would have none of it.
Similarly, in the movie, Steve questions why a beautiful woman would choose to join the Army, but he’s just being a dork and never gets an answer. He never repeats the question and we never do learn, just like we never learn how Falsworth, Dugan or Bucky joined up. Because you don’t need to know, you kind of figure they did it because that’s what they chose to do. It isn’t much of a mystery why the men would take up arms for their country, and the screenwriters don’t treat Peggy any different.