The U.S. European Command issued an "updated theater strategy" document Tuesday, pointing to Russian aggression as a top concern and warning that the U.S. troop drawdowns of the past 25 years put the region's stability at risk.

The 12-page document lays out EUCOM's priorities for the next three to five years and lists a dizzying array of challenges that include refugee migration, financial crisis, cyber attacks and infectious diseases.

The most prominent challenge is Russia and its "disregard for the sovereignty of its neighbors in Europe" as well as its military aggression beyond the EUCOM region, including Syria.

"Russia is presenting enduring challenges to our allies and partners in multiple regions; therefore, it is a global challenge that requires a global response," according to the report.

Tackling that challenge will require EUCOM to work carefully with other military components to ensure that "collective DoD deterrence efforts are synchronized and achieve the desired effect without causing unwarranted escalation or provocation."

Beyond the top concern of "deterring Russian aggression," EUCOM's other strategic goals include shoring up the North Atlantic Treaty Organization alliance, countering transnational threats and maintaining U.S. military readiness in the region.

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There are currently about 65,000 U.S. troops in Europe, down from a peak of more than 200,000 in the 1980s.

Despite Russian aggression, specifically its invasion of Ukraine's Crimea region in 2014, the Pentagon has been reluctant to divert more troops to Europe as new crises emerged in the Middle East and Pacific regions.

Yet EUCOM's new strategy warns that "fully addressing" Europe's security challenges "and their long-term implications requires a reformulation of the U.S. strategic calculus and corresponding resourcing levied towards Europe," the report said.

While the U.S. has been rotating some additional units into Eastern Europe in an effort to reassure NATO's easternmost allies closest to the Russian border, the report states bluntly that temporary presence "does not substitute for an enduring forward deployed presence that is tangible and real. Virtual presence means actual absence."

"Reduced U.S. forward presence and degraded readiness across the services are inhibiting the United States' ability to favorably shape the environment. The size of the military presence requires difficult decisions on how best to use limited resources to assure, stabilize, and support the USEUCOM mission in the new European security environment," according to the report.

The new strategy highlights Europe's geography as an essential staging ground for global operations. "U.S. infrastructure in Europe enables not only USEUCOM to meet its assigned missions, but it is also essential for the transit of forces and materiel through Europe to support other combatant command missions and requirements."