LIBBY GEORGE UNREST and violence are worsening across Nigeria, where gunmen in the northwest were reported to have kidnapped around 30 students from a forestry college overnight in the fourth mass school abduction since December. Growing public anger prompted President Muhammadu Buhari to replace his military high command earlier this year. Here is a summary of the violence: ARMED GANGS, NORTHWEST/NORTH-CENTRAL NIGERIA Armed gangs that rob and kidnap for ransom, commonly described as "bandits", are active across the northwest. Such groups killed more than 1,100 people in the first half of 2020 alone, according to rights group Amnesty International. In…