The number of roadside bombs doubled from the year before to roughly 2,000, with many of the devices more powerful than in previous years.
Unlike in 2007, when militants carried out ambushes only in small numbers, insurgents over the last year massed in groups of hundreds on multiple occasions. Some 200 militants nearly overran a small U.S. outpost in eastern Afghanistan in July, launching an early morning attack that killed nine U.S. troops.
U.S. forces suffered an average of 21 deaths in Afghanistan each month this year from May to October - by far the deadliest six-month period in Afghanistan for American soldiers since the 2001 U.S.-led invasion to oust the Taliban.
The U.S. now has some 32,000 forces in the country - record levels - and officials say those troops have moved into new territory and rousted militants in those regions.
But militants gained new ground in the south - even on the doorsteps of Kabul - and Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, announced on a recent trip to Kabul that Afghanistan could see up to 30,000 new forces in 2009.
Col. Jerry O'Hara, a U.S. military spokesman, said Afghanistan is a "work in progress" but that advances were made in 2008.
"New forces are going to be coming to Afghanistan and it's going to come with a pretty lethal punch, if a lethal punch is still needed, to ensure we have security so we can work on development and governance," he said.
In addition to the 151 U.S. troop deaths in Afghanistan this year, British troops suffered 50 deaths, and Canadian troops 28. Other countries in the 41-nation coalition lost 56 troops combined.
Afghan police again suffered gravely in the fight against Taliban and other insurgents. At least 850 Afghan police were killed over the last year, according to data compiled by The Associated Press. More than 925 Afghan policemen died in Taliban ambushes in 2007.
Overall, the AP recorded at least 6,340 insurgency-related deaths in Afghanistan over the last year. In 2007, AP recorded more than 6,500 deaths.
The AP count shows that U.S. and NATO military forces killed about 370 Afghan civilians during operations; Taliban and other militants killed about 770.
The AP count is based on figures from Western and Afghan officials and is not definitive. Afghan officials are known to exaggerate Taliban deaths, for instance, and NATO's International Security Assistance Force does not release numbers of militants it killed, meaning AP's estimate of 3,800 militant deaths is likely low.
The U.S. and NATO strategy relies on an increasingly capable Afghan army. But while the army is being recruited and trained - to an eventual strength of 134,000, up from about 70,000 today - the U.S. next year will send in thousands of new troops.
As those troops move into two provinces around Kabul, and into regions in the south long patrolled by British and Canadian forces, commanders say the level of violence will rise. The timing of some of the deployments is based on continuing improvement in the security situation in Iraq.
"If we get the troops, they're going to move into areas that haven't been secured, and when we do that, the enemy is there, and we're going to fight the enemy," Brig. Gen. John Nicholson, the top U.S. commander in southern Afghanistan, said in an interview.
"So at first you're going to see a spike in violence and fighting and, unfortunately, casualties," he added. "But on the back end of that when we've defeated the enemy ... we'll be able to introduce governance and development. But people need to understand that there will be an increase in fighting and casualties to get to the point."