Pakistan is reeling from yet another deadly assault, after militants wearing suicide vests rampaged through a police academy in the southwestern city of Quetta, battling for four hours before blowing themselves up and leaving more than 60 dead.
The ability of militants to breach security and kill with ferocity has confounded the country. Extremists have been carrying out numerous attacks for years, killing military personnel, police, school children and worshippers kneeling in prayer.
One reason is the sheer number and variety of extremist groups, some of which have been battling the military in a bid to bring down the government.
Another intertwined reason is the...