FORT POLK, La. — Shortly after dark, the paratroopers jumped out of C-130s into a Caspian Sea country teeming with mayhem, political unrest, and insurgents.
Their first mission was to prevent a US consulate from being overrun.
Then they were to repel an invasion by a hostile neighboring nation that was after oil wealth of the fictional country of Atropia. If all went according to plan, the mission would last no longer than a few weeks.
A protracted ground war this was not.
The training exercise — which kicked off in this Army base in Louisiana this month — is among the first the US Army has designed in an effort to overhaul the country’s fighting force as the war in Afghanistan draws to a close.
The withdrawal of US combat forces from Afghanistan by the end of 2014 will conclude a chapter of expensive and unpopular war in that country and in Iraq that began more than a decade ago and has led to the deaths of more than 6,000 American troops.
The new Army, senior military leaders say, must become more nimble, its officers more savvy, and its engagements more nuanced and almost certainly shorter. The lessons of the Arab Spring weigh heavily on war planners, with an array of threats looming in the Middle East and elsewhere. A high premium is being placed on devising the proper use of Special Forces, drones, and cyber capabilities.
‘‘My premise is that the world is going to get more complex, it’s going to get more difficult,’’ Army Chief of Staff General Ray Odierno said en route to Fort Polk, where he observed the first phase of the training exercise. ‘‘We’re going to need leaders who can be very adaptive.’’
The transition is fraught with challenges. The Pentagon has been ordered to slash its budget by $487 billion over the next decade. As part of that effort, the Army intends to shrink from its 2010 wartime peak of 570,000 active-duty soldiers to 490,000 in 2017.
After growing accustomed to largely unquestioned spending during the Iraq and Afghanistan wars, commanders will now face painful fiscal choices.
For the past decade, Fort Polk and other Army training centers have mainly prepared soldiers for the type of challenges they would face in Iraq and Afghanistan.
But it is hard to tell what the next major conflict will look like, so the new training exercises encompass an amalgam of threats, military officials say.
The soldiers involved in the exercise here are tasked with helping an allied nation push back an invading force, while battling two insurgencies. Special Forces working closely with conventional units and troops have been ordered to show deference to American civilian officials with vast experience in the country.
‘‘As we focus the Army for what we think the next conflict is going to look like, we need to be mindful that it will require closer cooperation among State, Defense, and intelligence agencies working together to fulfill the mission,’’ said Robert Mosher, a retired Foreign Service officer playing the role of an embattled consul general in the exercise.
To make the training more realistic, a would-be consulate was created as part of a fake village that had previously been built for the training of soldiers deployed to Iraq and Afghanistan. Surrounding woods became Atropia, a battlespace for roaming soldiers from the 82nd Airborne Division.
Colonel Bill Burleson, a commander at the Joint Readiness Training Center, said today’s Army is more battle-tested than it has been in decades. But the flurry of threats — ranging from hostile nations with nuclear programs, a possible war between Israel and Iran, and burgeoning insurgencies in North Africa and the Arab world — can be dizzying to contemplate, he said.
‘‘We’ve got tremendous operational experience after 10 years-plus of fighting,’’ he said. ‘‘What we’ve set out to do is put together a training exercise that trains for the uncertainty and ambiguity of the future.’’
A key challenge, Army officials acknowledge, will be retaining top talent as midcareer officers and enlisted soldiers mull new job prospects and the era of major land wars ends.
Frederick Wellman, a retired Army lieutenant colonel who runs a public relations firm focused on defense and veterans issues, said the thought of a peacetime job will probably be jarring for troops who have spent a decade at war.