The United States military is one of the most ethnically diverse and integrated institutions in the nation, and has long promoted racial equality. Yet in a string of cases in recent years, Americans bent on racist extremism have been current or former members of the armed forces.

The arrest of a Coast Guard lieutenant whom federal prosecutors accused last week of stockpiling weapons and planning to start a race war raised the question of whether the military, for all its efforts to fight discrimination, has a continuing problem with white supremacists in the ranks.

Here is a look at the issue and how the military has addressed it:

A Persistent Problem

Watchdog groups that monitor domestic extremist activity were quick to cite the allegations against the Coast Guard officer, Lt. Christopher Hasson, as a fresh cause for concern, one of a number in recent years involving people with military backgrounds. They have warned that the armed forces can be a training and recruiting ground for hate groups.

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“If you look at the list of domestic terrorism attacks, you will find a lot of veterans,” said Heidi Beirich, director of the intelligence project at the Southern Poverty Law Center.