"There is first of all fear ... that there could be a possible contagion," Romanian Foreign Minister Titus Corlatean told The Associated Press in an interview. "Romania is extremely preoccupied."
Specifically, concerns run high that after taking over the strategic peninsula of Crimea, Russian President Vladimir Putin may be tempted to try a land grab in Moldova, where Russian troops are stationed in the breakaway province of Trans-Dniester. It's one of several "frozen conflicts" across Eastern Europe whose ranks Crimea — many in the West now say with resignation — has joined.
In Romania, which neighbors predominantly Romanian-speaking Moldova, Monica Nistorescu urged the West to stand up to Putin — lest he come to view himself as unbeatable.
"The world should stop seeing Putin as the invincible dragon with silver teeth," said Nistorescu, "because we will succeed in making him believe that Russia is what it once was."
Across the border, Moldovan fears of Russian invasion were in no way theoretical: "We are afraid the conflict in Ukraine could reach us in Moldova," said Victor Cotruta, a clerk in the capital Chisinau. "Russian troops could take over Moldova in a day."
Many in the region are keenly aware that Poland had guarantees of military aid from France and Britain against Nazi aggression. But when Hitler invaded in 1939, France and Britain didn't send troops to Poland despite their declarations of war. That history feeds skepticism that NATO would come to the aid of eastern member nations in the event of a Russian attack.
"Poland's history shows that we should not count on others," novelist Jaroslaw Szulski told The AP.
Such feelings are particularly acute in the Baltic nations that are members of NATO and the European Union. Estonia, Latvia and Lithuania have sizable Russian populations that Moscow periodically declares it needs to "protect" — the key word Putin used in justifying its invasion of Crimea.
"I'm a bit skeptical," said Tiina Seeman in Tallinn, Estonia, when asked if she believed the West would come to her nation's rescue. "I'd like to believe so but I can't say I trust them 100 percent."
Moscow routinely accuses Estonia and Latvia of discriminating against their Russian-speaking minorities. Tensions between Russia and Estonia soared in 2007, when protests by Russian-speakers against the relocation of a Soviet-era war monument ended in street riots. Many Estonians blamed Moscow — which has handed out passports to ethnic Russians in the Baltics — for stirring up the protests.
As she arrived at an EU emergency summit on Ukraine last week, Lithuanian President Dalia Grybauskaite expressed more confidence than Seeman in the U.S.-led security alliance: "Thank God! Thank God that we are already 10 years in NATO!"
But she, too, expressed grave concerns about Russia's actions: "Russia today is trying to rewrite the borders in Europe after World War II."
History weighs heavily in Eastern European minds as they contemplate the future.
Many people see Russia's seizure of Crimea as similar to their experiences after World War II, when Soviet troops rolled through towns and villages, effectively putting them under the Kremlin's rule for decades.
"Of course there's a potential threat for us in the future," Katerina Zapadlova, a waitress in a Prague cafe, said with a bitter smile. She recalled how Soviet troops rolled into Czechoslovakia in 1968 to crush the Prague Spring liberalization movement.
"I'm afraid," she said, "It's because of what they did to us in the past."
Some experts say those fears are overblown.
"I wouldn't be afraid of Russian aggression in a short term," said Michal Koran of Prague's Institute of International Relations. "I'm 100 percent sure (that NATO would help its eastern allies). I think that NATO gets stronger as a result of the conflict in Ukraine."
Mutual economic dependence also lowers the likelihood of an armed conflict between Russia and the West. Russia's economy runs largely on the massive natural gas supplies it sells to Europe every year — and in 2012 it bought $170 billion in European machinery, cars and other exports. But it is also precisely the reliance of both eastern and western European nations on Russian energy that gives the West fewer options in taking a hard line against Moscow.
Romania's foreign minister also said that NATO has taken positive action in dealing with the Ukraine crisis, citing the dispatch of AWACS reconnaissance planes to fly over Poland and Romania to monitor the crisis.
"The measure taken by the North Atlantic Council aims ... to prevent tensions at a regional level and to guarantee the security of state members," Corlatean told AP.
Yet he, too, could not refrain from expressing historical fears, evoking the bloodbath that resulted when dictator Nicolae Ceausescu ordered troops to fire on protesters in the dying days of his regime.
"Romanians followed very closely everything that happened in these weeks, especially the dramatic events in Kiev," said Corlatean. "For us Romanians, this reminded us of the December 1989 revolution."
Some countries like Poland, which shares a border with both Ukraine and Russia, are already starting to take precautionary measures. Polish Prime Minister Donald Tusk has warned that instability in Ukraine may be prolonged and lead Warsaw to upgrade its weapons. At Poland's request, about 300 U.S. airmen and a dozen F-16 fighters arrived in Poland this week for a military exercise.
Tusk alluded to Europe's appeasement of Hitler and Stalin in the 1930s as he warned about the implications of letting Russia get away with its takeover of Crimea.
"Anyone who believes that peace and stabilization can be bought through concessions is mistaken," Tusk said last week in parliament. "Europe has made such mistakes, and they always led to a catastrophe."