NATO enlargement has been a contentious issue at times, not only among NATO members, but also with Russia, which sees the expansion of the alliance eastward as a threat.

• 北约扩展的行动已经多次引发争议，不仅在北约成员之间，还和俄罗斯发生争论。俄罗斯将北约向东扩展的行动看成是一个威胁。