WASHINGTON - The U.S. Army has prosecuted about 1,900 cases of desertion since 2001, even though tens of thousands of soldiers have fled the service in the face of deadly combat, long and multiple deployments in Iraq and Afghanistan, and strains on military families.

The number reflects how rarely the military takes desertion cases to court. And it underscores the complexities of such cases as a top military commander reviews the investigation of Sgt. Bowe Bergdahl, who left his Afghanistan post in 2009 and was captured and held by the Taliban for five years.

More than 20,000 soldiers have been dropped from the rolls as deserters since 2006, Army data show. Totals for earlier years weren't available but likely include thousands more.

In trial cases over the last 13 years, about half the soldiers pleaded guilty to deserting their posts; 78 were tried and convicted of desertion.

Desertion is relatively easy to prove, former Army lawyer Greg Rinckey said, but circumstances such as post-traumatic stress or family problems are also taken into account.

"A lot of deserters suffered from PTSD or other mental-health issues, or they were on their second or third deployment," said Rinckey. Numbers spiked as soldiers began returning to the battlefront, sometimes for stints up to 15 months.

Some disappearances involved divorce or sick children, he said. In other cases, soldiers deserted bases in the United States. Many are of these cases are handled without going to court martial, with soldiers administratively punished or sometimes medically discharged.

Soldiers who avoid deployment or leave posts in combat zones are more serious cases, particularly if the deserter is responsible for standing guard or protecting others in dangerous places.

"Those are looked at very harshly," said Rinckey, now a partner with the Washington law firm Tully Rinckey, "because commanders have a unit of other people who are looking at that soldier and saying, 'I don't want to go, either,' so obviously there has to be an example made."

Rinckey and other military officials say the Bergdahl case would be difficult. It's now in the hands of Gen. Mark Milley, head of U.S. Army Forces Command at Fort Bragg, N.C.

Even if Milley concludes Bergdahl deserted his post, he may consider mitigating circumstances.