The Russia-Ukraine war isn't what it was thought to be a couple of months ago -- a quick and narrow war confined to the two countries, ending with a few land concessions by Ukraine to Russia.

Instead, it's a prolonged war extended beyond the two countries and a proxy war between Russia and NATO. It's the Kremlin's apparent quest to change the world's geopolitical map.

Which country could be Russia's next target? How will the U.S. respond? What are the chances of the war spreading to NATO countries?

Here are some answers from experts in the field.

"The threat of the conflict spilling over to non-EU and non-NATO states is currently the highest and is already being increasingly felt in Moldova following the alleged 'terrorist attacks' between April 25 and April 28," Dr. Liana Semchuk, lead Europe and Eurasia analyst at U.K.-based strategic advisory firm Sibylline, told International Business Times.

"This likely indicates that Russia's military offensive is highly unlikely to conclude in the short term. Nevertheless, whilst Russian forces are preoccupied in the Donbas, an invasion of Moldova itself is highly unlikely. However, the eventual annexation of the breakaway Moldavan region of Transnistria is possible but is highly likely to be dependent on the outcome of the ongoing Russian offensives in Ukraine.

"As such, the evolving security situation in Transnistria is the most immediate flashpoint to watch for a potential further regional escalation, particularly as Russia increases its warnings to NATO against any involvement in Ukraine and signals the options available to the Kremlin to escalate the war if its warnings are ignored."

How would the U.S. respond in that case?

"The U.S. has been one of the leading nations calling for the expansion of sanctions against Russia and mobilizing support for Ukraine," said Semchuk.

"The trajectory of this sentiment is highly likely to only increase, should Moscow continue to expand its war aims. As this week's summit at Ramstein airbase in Germany has demonstrated, the U.S. is highly likely to continue pushing for more military aid to Ukraine.

"Notably, Secretary of Defense Lloyd Austin's statement on Monday that the U.S. 'wants to see Russia weakened' to the extent that it will be unable to repeat such military aggression as seen in Ukraine again is likely to have only reinforced the growing perceptions in Russia that the war in Ukraine is a proxy conflict between Russia and NATO."

What are the chances of the proxy war turning into an all-out war with Russia attacking a NATO country?

"The Russian military is highly unlikely to invade a NATO country," security and intelligence expert K. Campbell told IBT. "Such military action would require NATO and its individual members to invoke the North Atlantic Treaty's Article 5, which requires NATO members to consider an attack against one ally as an attack against all allies. While Article 5 allows each NATO ally to respond as it sees fit, Putin [and probably even NATO] doesn't know how NATO's 30 members would respond if he were to invade a NATO country. I think it's unlikely that [Russian President Vladimir] Putin and his generals want to risk the diplomatic, military, and economic wrath of 30 NATO members."

Juscelino Colares, a professor of business law and co-director of the Frederick K. Cox International Law Center, doesn't think Russia is in a position to take on NATO.

"Nine weeks into its war of aggression, a war that has seen the Russian military lose about one quarter [the U.S. estimate] of the combat force it had prior to invading Ukraine, Russia's military could hardly be ready for an attack on any NATO country without risking a major humiliating and disabling defeat," Colares told IBT.

"Other than threats of using nuclear war or firing a new generation of hard-to-defend missiles, Russia's depleted military also has a big morale problem that would only get worse should Putin decide on an expanded campaign against one of Ukraine's neighboring NATO countries.

"Western financial sanctions will also start taking a more serious bite once remaining supplies of spare parts dwindle, and Russia sees itself unable to import components essential to operating military hardware, such as microchips, which are mostly sourced abroad."