As a retired veteran who has been in a combat tour and been threatened by a subordinate soldier, I feel strongly that much of the blame for the series of incidents (murders of Afghan civilians, park ranger, suicides, etc.) rests with Congress.
The size of the military is too small to permit support of deployed combat forces, in terms of both numbers and duration, without multiple tours by individuals. The stress of each tour is great for both the soldier and their family. Repeated tours and the threat of repeated tours multiplies this stress, especially for those who live in the hostile environment for extended periods.
Congress controls the purse strings, thus troop strength, weapon development, medical support (including pressure to return people to full, unlimited duty), training and benefits.