The recent stream of senior U.S. defense officials to Nordic countries underlines American concerns about potential friction in northern Europe, and Washington's efforts to boost defense and deterrence there. Defense Secretary Ash Carter stopped in Norway in early September, while his deputy Bob Work, who has been to the region three times over the last two years, paid an early-October visit to Finland's capital, Helsinki. Shortly thereafter, Air Force Secretary Deborah James made her own trip across the region. (Go back to last year, and Senate Armed Services Committee chair John McCain was in Norway and Sweden to discuss regional security.)

The multi-country itinerary reflects the realization that boosting defense and security cooperation there requires more than a one-size-fits-all approach. For starters, Norway and Denmark are founding members of NATO and treaty allies of the United States, while Sweden and Finland are only NATO partners and have no formal defense agreement with the U.S.

Furthermore, the Nordic countries face very different challenges in the east and the north. Norway is primarily worried about its High North (the European Arctic), where the country shares a short border with Russia, and with Russia's northern fleet close by at Murmansk. Here, the defense challenges are fundamentally maritime in nature, as Russian forces must cross the Norwegian Sea to reach the broader North Atlantic. Just last week, the Sea saw the largest sortie of Russian warships since the end of the Cold War, as the Russian carrier Admiral Kuznetsov and its escorts transited the area on its way to the Mediterranean. To boot, NATO's maritime command has reported that Russian submarine activity is back to levels not seen since the early 1990s.

Sweden and Finland, meanwhile, are focused on the Baltic Sea region. NATO's Baltic members, Estonia, Latvia, and Lithuania, are some of the alliance’s most exposed allies, thanks to geography and the limited defense resources available to countries of only a few million people each. Moreover, Russia is developing a powerful anti-access/area-denial network that would make it difficult for NATO and the U.S. to reinforce the region were Moscow to launch an ambush on the Baltic states. Just recently, Russia moved nuclear-capable Iskander surface-to-surface missiles to its Kaliningrad enclave at the southeastern end of the Baltic Sea, with implications for all of northeastern Europe.

The Swedes and Finns believe that an isolated Russian attack on them is wholly improbable, but that they could easily be dragged into a confrontation between Russia and NATO over the Baltic States. And NATO and the United States recognize that working with Sweden and Finland in a crisis could be quite useful.

American engagement with the region has already led to practical results. The U.S. has upgraded the Norwegian signals intelligence ship the Marjata with new sensors, and U.S. Marines participated in the recent Norway-hosted Exercise Cold Response. Oslo and Washington are finalizing plans for a rotational presence of Marines in Norway, as well as the future of the Norwegian maritime patrol aircraft fleet that keeps an eye on the comings and goings of Russian submarines. And although Norway’s participation in the F-35 project predates the new tensions with Russia, it’s worth noting that the Norwegian Air Force plans to buy up to 52 Joint Strike Fighters, a substantial number for a country of only five million.

The United States has also inked defense cooperation agreements with Finland and Sweden, and while they are far from mutual-defense treaties, they do open the door for much deeper cooperation around exercises, training, capabilities development, and R&D. Sweden and Finland also figured prominently in the last two iterations of BALTOPS, the annual Baltic Sea exercise held by U.S. Naval Forces Europe-Africa. Recent BALTOPS have also featured B-52 bombers, a first visit of this American military crown jewel to the Nordic region.

In the Nordic countries, the United States has found willing and eager allies and partners who want to work closely with Washington to shore up the defenses in a region that is once again tense. But the cooperation is not without its kinks. Defense spending in the region remains below the NATO commitment level of 2% of GDP, with Sweden having provided only a marginal increase in spending after the Ukraine crisis. Norway's recently released long-term defense plan includes a more significant boost in spending, but it must of course be fully implemented and resourced. Meanwhile, Finland's sluggish economy is putting pressure on government finances. Washington would also like to see deepened cooperation among the Nordic nations. But regional cooperation efforts to date have been met with mixed results, and a string of failed joint procurement efforts.

Russia is paying attention to the deepening U.S. engagement with the Nordic region. As Bob Work was in Finland to sign the defense cooperation agreement with his counterpart, armed Russian fighter jets violated Finnish airspace twice in rapid succession. And when Sweden's parliament was close to voting on a host-nation support agreement with NATO earlier this year, the discussion was muddied by a Russian disinformation campaign with outlandish statements about what the agreement would mean for Sweden.

More remains to be done. For example, if Sweden and Finland are to be operational partners with the United States during a crisis, it will require not just joint exercises but contingency planning. Furthermore, the Baltic Sea region is woefully short on advanced air defenses, something that the United States could help rectify. Also, the U.S. Navy should plan on more substantial exercises in the Norwegian Sea and High North, as Russia’s northern fleet continues to step up its activities. Finally, Washington needs to consider how to add Denmark to its efforts of shoring up Europe’s northern flank. Since 9/11, Denmark has been a go-to ally for Washington for tough counter-terrorism and counter-insurgency missions, but its role closer to home in the new European security environment is less developed.

With a to-do list of this size, count on more senior U.S. visitors and an American presence in the region in the months and years to come.