A new study of the counterinsurgency operations conducted by British forces and U.S. Marines in southern Afghanistan suggests a difficult road ahead. Success will demand lots of troops, aggressive patrolling and persistence in the face of rising casualties.

Those lessons, drawn from the failures and successes of the bloody counterinsurgency campaign in southern Afghanistan, run directly counter to the signals being given by David Cameron, who has suggested a reduction in British forces in Afghanistan. President Obama has already ordered the first withdrawals of American troops from Afghanistan.

Public fatigue with the war is putting increased pressure on London and Washington to accelerate troop reductions and to limit the exposure of deployed troops to combat. To date, 1,648 American and 375 British troops have been killed in combat in Afghanistan.

But Britain and the United States, along with the rest of NATO, have already committed to military operations in Afghanistan at least through the end of 2014.

The new study by senior civilian analyst Mark Moyar, along with other, suggests that critical errors have been made by both Britain and the United States during the 10 year-long conflict in Afghanistan. After the initial U.S. intervention in late 2001 collapsed the Taliban regime, American troops, attention and money were shifted to Iraq, and the Taliban regrouped and pushed back into the vacuum.

In southern Afghanistan, British commanders assigned in early 2006 to Helmand Province were given only 3,150 troops and confusing and often conflicting directives on how to wage war. The initial mission was seen as a peace support and counter-narcotics operation, according to Daniel Marston, an adviser on counterinsurgency to the Royal Military Academy at Sandhurst.

Subsequent tactical directives veered between attempting to drive out the Taliban, and seeking to win local co-operation by distributing humanitarian and development aid.

In a separate study, Daniel Marston wrote, "The mission was originally presented as a peace support and counter-narcotics operation. This framing of the mission was primarily a matter of political expediency, but also showed a lack of understanding and historical knowledge of counterinsurgency on the part of both military and civilian officials.''

In the four years that undermanned British forces were trying to secure Helmand Province, the Taliban insurgency only gained ground. Under constant threat, local government could provide few services.

British troops, hunkered down in "platoon houses", were unable to mount regular patrols and were harassed by drive-by Taliban shootings. Dozens of key Afghan district and provincial leaders were assassinated. Without economic development, public support for the government ebbed.

With only one brigade deployed in the region, Moyar writes, "the British had too few troops to give both the enemy and the population the attention they needed, a fact that British officers reported to their civilian masters repeatedly.''

In 2010 a battalion of U.S. Marines arrived in the Sangin district of Helmand Province, taking over from British forces. They brought two advantages: more combat power, and the tactical freedom to focus on either killing the Taliban or stimulating local government, depending on local conditions. The Marines insisted that Afghan troops accompany them on all operations. They also abruptly stopped the practice of handing out development aid in the hope of earning popular gratitude -- an approach that clearly hadn't worked in Helmand or elsewhere -- "and instead made the aid contingent on support from the population,'' Moyar writes.

"With roughly the same number of troops as the forces they had replaced, the Marines gained control over the entire operational area in a period of three months and largely suppressed the insurgency by the time their seven-month tour ended,'' he adds.

In an interview with The Huffington Post, Moyar, a lecturer at the U.S. Marine Corps University , stressed that whatever mistakes were made at the top, battlefield commanders and the troops fought with skill and determination. "It's not like the British were stupid,'' he said. "There were certainly some who had a better idea of what needed to be done.''

The conclusions of a senior British commander quoted by Moyar seem to sum up both the allied approach to the war in Afghanistan and as a caution about future military missions.

"We didn't realize the complexity and the character of the context in which we were going to fight,'' Moyar quotes Rear Adm. Chris Parry, one of the senior British planners, as saying. "In fact, we didn't envisage we were going to fight. I think we took too much baggage with us from previous experience from Borneo, Malaya and Northern Ireland, and we hadn't really recognized that the lessons we had taken from those campaigns were valid, but they weren't sufficient for the context of Afghanistan.''