Complex sentence: US forces entered the war in Afghanistan in 2001, although there was fierce fighting such as the Battle of Tora Bora and Operation Anaconda the IED threat remained generally low until later in the war.
Split into simpler sentences: US forces entered the war in Afghanistan in 2001. Although there was fierce fighting such as the Battle of Tora Bora and Operation Anaconda, the IED threat remained generally low until later in the war.