CNN
 — 

The threat of ISIS, also known as Islamic State, might have seemed to be waning as headlines turned to Ukraine, Gaza and the next US election. But last week’s attack on a Moscow concert hall reminded the world of the enduring danger of Islamist terrorism and the ambitions of what is known as IS Khorasan (ISIS-K) far beyond its camps in the mountains of Afghanistan.

Analysts believe the group has a growing focus on Europe – and point to events such as this year’s Paris Olympics as potential targets.

ISIS claimed responsibility for the Moscow attack. The fact that Tajik nationals were allegedly involved…