Russia continues to issue threats to countries on its borders — most notably those with significant populations of ethnic Russians like Georgia and Ukraine which have already felt Moscow's wrath in recent years.
But many European countries have reduced their spending in the decades since World War II, so preparing for a potential war with their aggressive and highly militarized neighbor is not as simple as giving their soldiers MREs, bullets, and marching orders.
And while the U.S. helps guarantee the security of NATO members, a recent analysis by the RAND Corporation indicates that many countries on the eastern front could be swallowed up long before American reinforcements could arrive. Some countries, like Estonia, could be conquered in as little as 60 hours, analysts say.
Here's what eight countries in Eastern Europe are doing to get ready for the war they hope never comes:
1. Ukrainians are hastily emplacing fixed defenses
Ukrainian soldiers practice clearing trenches on Nov. 2 during an exercise in Ukraine with U.S. soldiers. (Photo by Staff Sgt. Elizabeth Tarr)
Ukraine is the one state on the list who is currently engaged in a war with Russia. While their troops have fought limited groups of Russian "volunteers," Ukraine's top generals are worried about a full-scale air attack and ground invasion.
To prepare, they're digging trenches and emplacing fixed defenses like tank traps and bunkers. They've also practiced maneuvering mobile air defenses and other units. Finally, Ukraine is planning a massive expansion of its navy to replace many some of the ships captured by Russia in the 2014 annexation of Crimea.
2. Estonia is training a guerrilla force to bleed Russian occupiers dry
Estonian soldiers provide cover fire for U.S. paratroopers on Nov. 3, 2016, in Hellenurme, Estonia, during a joint training exercise. (Photo: U.S. Army Pfc. James Dutkavich)
Estonia fields an army of only 6,000 soldiers and fully expects to be overrun within days if attacked by Russia, an outcome that the RAND Corporation agrees with. But Estonia plans to make the Russians regret ever acre they took.
The nation is hosting "military sport" contests and encouraging citizens to keep weapons in their homes. The sports events include 25-mile ruck marches, evasion exercises, plant identification, and others which test skills useful for an insurgent force. Over 25,000 Estonians have joined the weekly drills.
3. Latvia is training up a "home guard" and investing in special operations
Latvian soldiers drive their armored combat vehicles into position during a joint training exercise with U.S. troops on Oct. 31, 2016, in Adazi, Latvia. (Photo: U.S. Army)
Like Estonia, Latvia is bullish on training citizens to resist an invasion. They're moving forward with plans to allow "home guard" member to keep their weapons and night vision devices in their homes. They're also betting heavily on special operations forces, tripling the size of the National Armed Force Special Operations Forces.
Like most NATO members, they're also trying to get more NATO troops on their soil to deter Russian aggression in the first place. Britain is already sending troops for exercises, and Denmark and France have promised forces as well.
(Photo: U.S. Army Pfc. James Dutkavich)
Lithuania has distributed a civil defense book to its citizens which details how to survive a Russian invasion that includes a phone number which residents can call to report suspected Russian spies. It is also planning to restart military conscription for men between the ages of 19 and 26.
Norwegian soldiers prepare for a stalking event during the 2016 Best Sniper Squad Competition in Germany. The team went on to win the overall competition. (Photo: U.S. Army Spc. Emily Houdershieldt)
Norway officially acknowledged that it believes Ukraine was illegally occupied by Russia during a state visit to Ukraine on Oct. 18. Russia later added Norway to its list of targets for "strategic" weapons. Russia uses the word "strategic" to differentiate between conventional and nuclear-capable forces.
Norway has invited more NATO troops, including U.S. Marines, to train there. It's also stepped up its intercepts of Russian aircraft flying near its shores. Norway's F-16s now maintain a 24-hour alert. The country is also re-opening Cold War-era bases in the far north.
6. Poland is buying massive amounts of equipment, including new subs
Polish soldiers of 17th Wielkopolska Mechanized Brigade move a simulated wounded soldier during a react to contact scenario during exercise Combined Resolve VII at the U.S. Army's Joint Multinational Readiness Center in Hohenfels Germany, Sept. 12, 2016. (Photo: U.S. Army Spc. Gage Hull)
Poland, which is considered to be one of the more hawkish NATO members, has been warning of a threat from Moscow for some time. For the past few years, it has championed regional security agreements with its neighbors and worked hard to ingrain itself with NATO.
Since Russia invaded Ukraine, Poland has ramped up the purchase of military hardware such as new, stealthy submarines and Polish-manufactured S-70 helicopters for its special operations soldiers.
7. and 8. Finland and Sweden are securing defense agreements with the U.K. and U.S.
Finland and Sweden are countries which famously prefer to avoid alliances, but Russian aggression has spurred an interest in limited defense agreements which will make it easier for NATO troops to deploy to those countries in the event of war.
The U.K. and U.S. signed two contracts each with Sweden and Norway, and all four agreements have different details. But, the broad strokes are that all four countries will increase their interoperability by holding joint training exercises as well as participating in research, development, and procurement projects.