Under our wing: a NATO air-policing mission over Lithuania, May 2015.

In May 2013, when I became commander of U.S. European Command and NATO’s supreme allied commander for Europe, I found U.S. and NATO forces well suited for their requirements at the time but ill prepared for the challenges that lay ahead. The United States’ military presence in Europe, which had shrunk significantly since the 1990s, was not oriented toward a specific threat. NATO, for its part, was mostly involved in operations outside the continent, primarily in Afghanistan.

Now that I have completed my tenure, I have the chance to reflect on how U.S. European Command and NATO have evolved since I took up my positions. Over the past three years, the United States and the alliance have shifted their focus to threats closer to the heart of Europe—namely, Russian aggression and the vexing challenges associated with the ongoing instability in the Middle East and North Africa.

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