Putin's invasion of Ukraine is seen as his biggest ever mistake — and it will harm Russia for years to come

Russian President Vladimir Putin has been in power for more than two decades and during that time has carefully cultivated an image of himself as a tough, strongman leader, fighting for Russia's interests and reinstating the country as a geopolitical and economic superpower.

With his decision to invade neighboring Ukraine, however, analysts say Putin has made the biggest mistake of his political career and has weakened Russia for years to come.

"Everything he has done up to this point [conferred] reputational damage to Russia, but it also enhanced power. And he just kept going and kept going and kept going," Kurt Volker, former U.S. ambassador to NATO, told CNBC.

"But now he has actually dramatically weakened Russia, in every respect," he said, adding that he could not think of anything that Putin has done in his political career that's comparable.

Global leaders are gathering in Europe on Thursday to discuss the war in Ukraine and how to help the country survive Russia's onslaught: An extraordinary NATO summit in Brussels, as well as meetings of EU leaders and the G-7.

NATO is expected to commit to "major increases" in troop numbers along its eastern flank as well as more arms and humanitarian assistance for Ukraine, although the military alliance has been reluctant to go further, fearing a direct confrontation with nuclear power Russia.

Speaking to CNBC on Thursday, NATO Secretary-General Jens Stoltenberg said, "President Putin has made a big mistake and that is to launch a war, to wage a war, against an independent sovereign nation."

"He has underestimated the strength of the Ukrainian people, the bravery of the Ukrainian people and armed forces," Stoltenberg told CNBC's Hadley Gamble.

NATO's plans to step up support for Ukraine, and deployments in Eastern Europe would allow it to respond to "any threat, any challenge, to our security."

Russia's invasion of Ukraine has, in one month, prompted more than 3.5 million civilians to flee the country, with hundreds of thousands losing their homes in a relentless bombardment by Russian forces.

The southern city of Mariupol has been the worst hit so far, with the port — a key export hub for Ukraine — still under siege and heavily destroyed.

Ukraine's president, Volodymyr Zelenskyy, has said there are around 100,000 civilians still trapped in the city, where water, food, electricity and medical supplies are scarce.

Despite deploying near-constant shelling attacks and siege tactics in some areas, Russian forces have only captured one city — Kherson — and a much-feared assault on the capital Kyiv has yet to begin. In addition, the country's second-largest city, Kharkiv, continues to resist Russian attacks and the western city of Lviv is currently relatively unscathed.

The U.K. Defense Ministry said Wednesday that little had been gained by Russian forces, despite attempts to envelop Ukrainian troops in the east of the country.

In a statement, Blinken compared the destruction in Mariupol to similar Russian campaigns against Grozny in the Second Chechen War and Aleppo during the Syrian civil war.

"Russia's forces have destroyed apartment buildings, schools, hospitals, critical infrastructure, civilian vehicles, shopping centers, and ambulances, leaving thousands of innocent civilians killed or wounded," he said. 

Russia has repeatedly said it does not target civilian infrastructure, despite much evidence to the contrary. CNBC has contacted the Kremlin for a response to the U.S. accusation that Russia has committed war crimes and is awaiting a reply.

Under Putin's leadership — and until now — Russia's economy has prospered.

Putin attracted much foreign direct investment to the country and exploited its natural resources, particularly its abundance of oil and gas, as well as trying to diversify the economy.

During his tenure, however, Russia has also been hit by economic misfortunes both of its own making — such as international sanctions after its 2014 annexation of Crimea from Ukraine, a nerve agent attack in the U.K. and its meddling in the 2016 U.S. election — and some it had no control over, such as the 2008 financial crisis, 2014 oil price crash and most recently, the Covid-19 pandemic.

Now, Russia's economic misfortunes are once again ones that Putin has brought upon the country himself with the invasion of Ukraine.

The economy is already creaking under the weight of international sanctions and on Thursday, when U.S. President Joe Biden meets with European and NATO leaders in Brussels, even more sanctions could be imposed squeezing energy exporter Russia hard.

The Institute of International Finance has said it expects Russia's economy to contract by 15% in 2022, driven by both official sanctions and the "self-sanctioning" of foreign companies that have pulled out of Russia.

Predicting a further economic decline of 3% in 2023, the IIF said Wednesday that the war "will wipe out fifteen years of economic growth." Moreover, it said the impact on medium- and long-term prospects is likely to be even more severe, with a "brain drain" and low investment likely to weigh heavily.

Despite making limited progress in his invasion so far, Putin appears undeterred.

Russian forces are now believed to be conducting a period of reorganization before resuming large-scale offensive operations on and around Kyiv.

Taras Kuzio, a research fellow at the Henry Jackson Society, wrote in an article for the Atlantic Council on Tuesday that it is "increasingly obvious that Russian President Vladimir Putin has badly miscalculated."

'He appears to have sincerely believed Kremlin propaganda fairytales about the weakness of the Ukrainian military and the readiness of ordinary Ukrainians to welcome his invading troops with cakes and flowers," Kuzio said, stating that Putin had drunk the Kremlin "kool-aid."

In addition, Putin seems to have been unprepared for the ferocity of the international response or for the scale of domestic opposition to his invasion, Kuzio noted. "Thanks to these catastrophic miscalculations, Putin now finds himself with no good options to end a war that is threatening to accelerate Russia's geopolitical decline as a great power."

Russia has few friends left on the global stage, with the invasion almost universally condemned. Even Russia's ally China appears uneasy about the potentially prolonged conflict in Ukraine and its impact on the global economy.

When the U.N. General Assembly met in early March, 141 countries adopted a resolution demanding that Russia immediately end its military operations in Ukraine. Only a handful of countries — a rogue's gallery of Belarus, North Korea, Eritrea and Syria, all of which are run by dictators — supported Russia's invasion. Russia's allies Cuba, Nicaragua and China abstained in the vote.

Close watchers of Putin say there are increasing signs of desperation in Russia's military campaign and have questioned how far Putin will go to achieve his objectives.

"There are deep mysteries about Russian intentions," Ian Lesser, vice president of the German Marshall Fund of the U.S., told CNBC earlier this month. "How far will they go? What would they consider a victory?"

"There are all sorts of possibilities, from a complete occupation of Ukraine, which I think most observers would say is not possible, to control over a couple of critical political centres in Ukraine, including Kyiv and possibly including Odesa, or perhaps they take have a larger territorial gambit in mind."

In such a scenario, he said Russia would be "very exposed" to an ongoing insurgency which also implies ongoing humanitarian costs. "So there are large dilemmas here," Lesser added.

Michal Baranowski, senior fellow and director of the German Marshall Fund's Warsaw office, told CNBC on Tuesday, that Putin has "really overextended himself."

"We might be looking at the end of Russia as we have known it," he said. "But if he survives this, I think what we might be looking at is the foothills of a new Cold War."