WASHINGTON — Melissa Gauntner, a retired Army first sergeant, has at times been gripped with panic and has trouble socializing beyond close friends, the result of dual traumas: years of sexual assault and harassment in the military, and mine explosions she saw in Afghanistan.

Jen Burch, once an active runner, developed breathing problems after she was exposed to toxic burn pits in Kandahar, Afghanistan.

Isiah James, who served in Iraq and Afghanistan, keeps a knife in his shower, ever on guard.

Thousands of veterans who served in the wars that began after the Sept. 11, 2001, attacks struggle with issues that are often invisible to those around them. Some are suffering from health problems and trauma, and others from feelings of displacement and alienation, which for many grew more intense as the United States completed its withdrawal from Afghanistan last month and the Taliban regained control of the country.

“It is one of those things you have to leave in God’s hands,” Ms. Burch said of her health issues. “To someone looking at me, I look like a very healthy 34-year-old woman, and I am not.”

Watching Kandahar, where she had tried to make a difference, and then the entire country quickly fall to the Taliban exacerbated her pain.

“It all feels like a complete failure,” she said from her home in Washington, D.C. “I have my own demons from my time there, and I worry about other veterans and the defeat they must be feeling.”

Some veterans are wondering if the wars were worth it, said Bonnie Carroll, the founder of the Tragedy Assistance Program for Survivors, a support organization for those grieving the death of a service member.

“In World War I and World War II, if you died, you most likely died on the battlefield,” she said. “But many of our loved ones are now bringing the war home with them and dying from suicide as a result of post-traumatic stress or illness as a result of exposures.”

Ms. Burch, who was a staff sergeant in the Air Force in Kandahar from 2010 to 2011, often walked by pits filled with garbage, equipment and other waste. She said the doctors who examined her in 2014 found ground glass nodules in her lungs, which must be monitored for cancer. She now regularly uses an inhaler.

U.S. officials estimate that more than 3.5 million service members who deployed were exposed to toxic smoke from the roughly 250 pits used in Iraq and Afghanistan. President Biden has said that he believes toxic substances from burn pits contributed to the brain cancer of his son Beau, who served with the Delaware Army National Guard at Balad Air Base in Iraq and died of the illness in 2015.

Even as they struggle, veterans are having more open discussions about their experiences and mental and physical conditions.

“I was too close, too much in love with my war,” said Maj. Thomas Schueman, 38, a Marine Corps commander who is now studying at the Naval War College. As time passed and he realized that the war in Afghanistan was essentially lost, “I started to maybe come to terms with the reality,” he said. “I am still fighting a little bit of that war, inside.”

Julie Howell, an Army specialist from 2000 to 2005 who deployed to Iraq, said she was always going to join the military.

“My grandpa and grandma met at a U.S.O. dance,” she said.

She enlisted at 17 and became quickly disenchanted.

“I am just coming to terms with the sexual violence I experienced,” said Ms. Howell, 38, who lives in El Paso. “You expected your battle buddy to bring you back to your room, not take you to their room.”

She added, “I don’t think civilians have a clue about this, and part of that is our own silence.”

In interviews, scores of female veterans shared stories that were remarkably similar if distinct in the details: attacks or coercion by men they served with, sexual encounters they felt pressured to have, abuse suffered in formation the next day.

For the past 10 years, the military has tried to make progress against sexual assault in the ranks. The Pentagon and Congress are poised to change how sexual assault cases are adjudicated by taking their prosecution out of the hands of military commanders, which many survivors say would reduce retaliation and increase convictions.

Ms. Gauntner, 40, who retired this year after 21 years in the military and three combat deployments, described the harassment she repeatedly faced.

“I had a situation where I was roofied,” she said. “I had a platoon sergeant massage my shoulders when he was showing me to my room. I had my basic training drill sergeant ask me if I had ever been with a Black man. I had a platoon leader who put his hand up my skirt.”

Ms. Gauntner went through a therapeutic program “where they show you that not everyone is a threat,” she said. She left incredulous.

“It is exhausting to stay on guard all the time,” she said. “But it is needed.”

Mr. James, 40, said he joined the Army “because I was poor.” He served in the infantry from 2005 to 2013, twice in Iraq and once in Afghanistan.

“There wasn’t a day that went by that I did not fire my weapon in combat,” he said.

Between his last two deployments, he was hospitalized in Germany for post-traumatic stress. He pondered suicide at least once back in Brooklyn. “When I got out of the service is when everything hit me,” he said.

“It’s not natural for a human being to take a life from another human being. It’s not natural to see children not as children but as a target,” said Mr. James, who is now a policy adviser for the Black Veterans Project. “I used to sleep with a gun under my pillow. For the first two years of marriage, I didn’t sleep in the bed; I slept on the couch to guard the door. I still carry those things with me. I was 90 percent disabled at 26 years old. People don’t understand how much fighting I have seen.”

Geoffrey Easterling was an officer in the 3rd Cavalry Division in Afghanistan. He said he loved his time in the military, but service members needed better basic mental health preparation.

“Right before we were deployed, I went to a service and the chaplain told us, ‘You’re going to go home and either want everyone to touch you and hug you, or everyone to leave you alone,’” he said. “That should be told to every soldier, to make sure those things are clear.”

Some veterans feel disconnected from community and lack a sense of purpose when they return home.

“When you tell a progressive you served in a war, they look at you as if you were a gang member, and they look for an explanation as to why you joined,” said Adam Weinstein, a research fellow at the Quincy Institute and a Marine veteran. “Conservatives will often shower praise on you and put you on a bizarre pedestal. Neither of those interactions feels particularly authentic.”

In military families, scholars find what they call secondary traumatic distress, symptoms of anxiety stemming from a service member’s combat-related trauma and complicated feelings about family traditions that compelled many to serve.

June Heston’s husband, Mike Heston, died in 2018 of cancer that doctors said was related to exposure to toxins during his deployment with the National Guard. “He was the soldier and if asked to go again would have,” she said. “It was hard for him, a man who loved his country and our military, to tell our son, ‘Do not join.’”

The number of calls to a crisis hotline for veterans has increased in recent weeks, a spokesman for the Department of Veterans Affairs said, adding that it was not clear whether it was related to the situation in Afghanistan.

“It’s entirely natural to feel a range of emotions about the latest developments in Afghanistan, and if you are feeling depressed, angry, heartbroken or anything else,” Denis McDonough, the secretary of veterans affairs, said in a statement.

Veterans grappling with the effects of 20 years of wars are reaching beyond the battlefield by running for office, trying to shape foreign policy and pushing legislation to enhance benefits. New organizations for veterans focused on community service, education and political engagement have begun to replace older and less diverse groups.

The wounds of this generation are deep, said Peter D. Feaver, a professor of political science at Duke University. “We should not pretend they are not.”

“But nor should we pretend this prevents society from moving forward or that it is paralyzing,” he added. “These are the same issues the Greatest Generation had to wrestle with, and what we have learned is that even wounded people can accomplish a great deal.”

Major Schueman said he had worked through his experiences with death and disappointment through literature like “The Things They Carried,” the 1990 Vietnam War rumination.

“I think young men that join the infantry want to validate themselves under fire. You don’t have time to feel. It comes down to Kipling’s ‘If—,’” he said, referring to the poem published in 1910. “If I can keep my head, right, I can have equanimity at all times in the middle of the storms.”

Seeing the current state of Afghanistan “causes an immediate emotional reaction,” Major Schueman said, “and then I have to immediately separate it. Because it is a spiral of doom, a cycle of death, and I cannot go there.”