A sombre mood has descended over KyivThe capital of Ukraine.. Across the city, people are preparing emergency supplies. There is only one topic of discussion on the streets of the capital: the possibility of war. 

Just over 200 miles away, Russian troops are gathering on Ukraine's snowy eastern border. Many fear they are awaiting orders to invade.

Today, senior US officials will meet with their European allies in Berlin amid fears that Russia could attack at "any point". 

Moscow has issued a series of demands to the West. Russian president Vladimir Putin wants to make sure that Ukraine never joins Western military alliance, NATOThe North Atlantic Treaty Organisation was founded in 1949 to unite Western democracies in Europe and North America against the perceived growing threat of the USSR. It now has 31 members.. He also wants NATO to stop military activity in Eastern Europe. The West has refused.

Last week, peace talks failed. Now, with 100,000 Russian soldiers closing in on Ukraine, fears are growing. If war breaks out, it will be the first major conflict on European soil since the Balkan wars of the 1990s. 

Some Western officials believe Russia is looking for an excuse to invade the former SovietRelating to the Soviet Union, a powerful group of communist republics, the biggest being Russia, that existed from 1922 to 1991.  republic. Critics say Putin's motives are clear: last year he published a 5,000-word essay calling Russians and Ukrainians "one nation". 

Russia denies it is planning an invasion, but Putin has warned that he will take "appropriate retaliatory military-technical measures" if his demands are not met. One pro-Putin newspaper even claims that Russia "will bury Europe and two-thirds of the United States in half an hour" if NATO is enlarged. 

Since 2014, conflictA state of disagreement when there is a difference of interests, values or goals. in eastern Ukraine has killed 14,000 people and displaced 1.4 million more. This week, Ukraine's defence minister told the West that an invasion would lead to bloodshed and a refugee crisis. "Tens of thousands could die," added one British minister yesterday. 

"To think that war could be contained to one nation would be foolish," said one intelligence official. 

But Western leaders still hope that Putin can be persuaded to call back his troops. Yesterday, US Secretary of State Antony Blinken called for a "diplomatic and peaceful path" forward during a visit to Kyiv. 

Others think sanctionsEconomic measures designed to punish a country, for instance by excluding it from trade. could stop Putin in his tracks. "Renewed military action against Ukraine would be a riskier step than any Putin has taken in 22 years as Russia's paramountMore important than anything else. leader," declared the Financial Times. 

Russia's annexationIn 2014, Russia invaded and took over the control of the Crimean peninsula from Ukraine. It has occupied Crimea ever since.  of Crimea in 2014 was largely a success for Putin. His poll ratings soared and Ukraine's attempts at Western integration were stopped.

But a full-scale invasion could be more costly. So far, the country has coped with Western sanctions, but more aggressive economic measures could be hugely damaging. 

If large numbers of Russian troops are killed, Putin may lose his popular support at home. And war may bring NATO and Ukraine closer together, not push them further apart.

Some think the costs of war could stop Putin. Others think he is determined to act. One thing is clear: war in Europe could have dire consequences not only for Ukrainians but for the entire continent - and even the world.

Yes: There is still hope. A combination of peace talks and economic sanctions could persuade Putin that the risks of war are too great to continue. An invasion is not inevitable.

No: Nothing will stop Putin from pursuing his goal of invading Ukraine and creating a new Russian superstate. Last minute talks are doomed to fail.

Or...? No one can say for sure what Putin's intentions are. The build-up of troops may simply be an attempt to bully Ukraine into giving up its goal of Western integration, not an indication of war.