Dagestan, in southern Russia, has a history of violence. Why does it keep happening?

The map above locates a June 23 rampage by Islamic militants who authorities say killed 20 people, most of them police, and attacked houses of worship in apparently coordinated assaults in two cities. (AP Digital Embed)

Over the years, Russia's southern republic of Dagestan, located in the North Caucasus region, has been beset by extremist violence. This weekend, there was more bloodshed.

Officials say five gunmen in the regional capital of Makhachkala and the city of Derbent opened fire at Orthodox churches and two synagogues, as well as a police post, killing at least 20 people before being slain by authorities.

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