WASHINGTON — A smaller share of Americans currently serve in the Armed Forces than at any other time since the era between World Wars I and II, a new low that has led to a growing gap between people in uniform and the civilian population, according to a new survey.

At any given time in the past decade, less than 1 percent of the American population has been on active military duty, compared with 9 percent of Americans who were in uniform in World War II. As a result, there is a growing generation gap, with younger Americans far less likely than older ones to have a family member who served.

The survey, by the Pew Research Center, found that while more than three-quarters of Americans over the age of 50 had an immediate family member who had served in the military, among Americans ages 18 to 29, the share was only a third. About 6 in 10 of those ages 30 to 49 have a family member who served. Part of the difference is years. Older people are more likely to have a spouse or a grown child, giving them more opportunities to have a family member who served. But the age gap persists, even when controlling for this, according to the survey.

The result is a military far less connected to the rest of society, a condition that some academics have said might not bode well for the future of military-civilian relations (the military is run by civilians). Others have warned that less connection between the military and the rest of society could lead to less-informed decisions about whether to go to war, because conflicts and the people who fight them are not part of most people’s everyday lives.