Western intelligence officials repeatedly said over the weekend that Russian forces have encountered "stiffer than expected" resistance from an outmanned and outgunned Ukrainian military.

As a result, Russia has thus far failed to take key cities across Ukraine, including the capital Kyiv. On Sunday, Ukrainian forces successfully repelled a Russian advance on a strategic airfield near Kharkiv, Ukraine's second-largest city, which has been under near-constant attack.

However, the situation on the battlefield could change very quickly as Russian forces keep up their assault. They still greatly outnumber Ukrainian forces, and Russia continues to maneuver its units into position around major urban centers.

A senior US defense official reportedly said on Sunday that Russia has only used two-thirds of the total combat power applied to the mission, leaving a significant amount of forces available to press the offensive.

And on Monday, a miles-long convoy of Russian military vehicles was bearing down on the Ukrainian capital, Kyiv, while intelligence also suggests Belarus is prepared to join the Russian invasion.

Putin, who probably thought Ukrainians would greet his tanks with flowers, might have misjudged not only the country's ability and will to defend itself, but also just how hard a line the international community would take against Russia in the face of an invasion.

For years, the Russian president has faced very little pushback from the West over his annexation of Ukraine's Crimea peninsula, his brutal support for the Syrian regime, and aggression in Georgia.

All their strong words aside, Western countries still bought gas from Russia, offered a safe haven to its rich oligarchs, and retained relatively normal diplomatic relations with Moscow.

But this time, the Western world and its allies are united like never before. From unprecedented sanctions that are already hurting the Russian economy to international sport slowly departing from the regime, even Switzerland will forego its famous neutrality.

"Russia's attack is an attack on freedom, an attack on democracy, an attack on the civil population, and an attack on the institutions of a free country. This cannot be accepted regarding international law, this cannot be accepted politically, and this cannot be accepted morally," Swiss Federal President Ignazio Cassis said.

"To play into the hands of an aggressor is not neutral. Having signed the Geneva convention of human rights, we are bound to humanitarian order. Other democracies shall be able to rely on Switzerland; those standing for international law shall be able to rely on Switzerland; states that uphold human rights shall be able to rely on Switzerland."

By Sunday, four days after the Russian attack began, at least 200,000 Ukrainians (mostly children, women, and elders), had entered Poland. Men considered fit for military service are currently not allowed to leave the country.

However, estimates by the United Nations and refugee organizations say the number of people who want to flee the Russian invasion can be as high as 4 to 7 million. How many will actually try to cross Ukraine's borders depends entirely on how the war develops.

However, experts think it's certain that arrivals will far exceed the so-called "refugee summer" of 2015, when about 1 million refugees and asylum-seekers arrived in Central Europe (primarily Germany) from Syria's war zone.

But the European Union promised that all war refugees from Ukraine will be accepted into its territory.

"It's war in Europe again for the first time, and that is also leading to a different way of thinking among member states," German Interior Minister Nancy Faeser said at a meeting with her European counterparts in Brussels, calling it a "total paradigm shift."

Evelyn Farkas, who served as deputy assistant secretary of Defense for Russia, Ukraine and Eurasia from 2012 to 2015, thinks that Putin’s endgame is nothing short of a revanchist imperialist remaking of the globe to take control of the entire former Soviet space.

"He has complete disregard for international law, norms and human rights and will only be stopped by maximum economic, political and military pressure," Farkas told Politico. "Russia is ... a rogue state on par with North Korea and Iran. Now, it is our obligation to protect the Ukrainian people and government, to do better in terms of helping them secure their airspace and to launch an active insurgency."

In addition, Farkas believes the West must slap the toughest sanctions on Russia. "We can blunt the impact to allies and partners dependent on Russian oil and gas by launching a Berlin airlift of fuel and pulling out all the stops to avoid this war from spreading to NATO territory and becoming a world war."