The existence or perceptions of threats can be another factor for regional organizations. If there is an actor within or outside the region, that threatens or is perceived to threaten regional states, it might be an important reason bringing states together under the umbrella of a regional organization. The perceived socialist threat became the major factor for the formation of NATO. The perceived German threat was important for the formation of both NATO and the EU because it was believed that German nationalism could only be weakened by engaging with Germany.

The correct choice is B.