For the most part, Russia has remained unconquerable. The only exception to that was the Mongol Horde. From 1242-1480, the Mongols, or Tatars, ruled Russia. That's how far back you have to go to find something of a successful invasion that led to a wholesale overthrow. The more modern example of an invasion is Napoleon's in 1812, which was a total disaster. Yes, the French were able to defeat the Russian armies multiple times, but he was never able to clinch a decisive win. He did reach Moscow, only to find it burned to the ground—completely inhospitable for the winter. The long retreat West saw his armies harassed by Russian troops in hit-and-run attacks. They were not equipped for the harsh winter. Disease set in, and Napoleon eventually abandoned his army. Of the 600,000 men who entered Russia, 400,000 became casualties. The point is Russia's massive landscape has been its best defense, and it would seem in 2022—it has forgotten that aspect with this venture in Ukraine.
The landscape would serve again as Russia's biggest defensive asset against the largest invasion force ever assembled in human history. Nazi Germany allocated some 4 million men, 3,000-5,000 aircraft, and close to 4,000 tanks to attack Russia along a near-2,000-mile front in 1941. Adolf Hitler's Operation Barbarossa was initially very successful, virtually destroying all Soviet armies west of the Ural Mountains, but like Napoleon—the weather and the landscape soon swallowed them up.
In Ukraine, Russia mobilized only 190,000 men, which is not enough. Hitler's 4-million-man force in Barbarossa wasn't enough either. They were also getting swallowed up by the land.
If you Google Kyiv and elsewhere in Ukraine, you have the major cities and then a whole lot of rural land, which can probably hide scores of insurgents should the capital fall. Right now, the Ukrainians and the Russians are holding peace talks along the Belarusian border, which I'll say probably isn't the best idea since Belarus declared it'd invade to help Russia some 36 hours ago.
Vladimir Putin tried to blitzkrieg the Ukrainians. It didn't work. The Ukrainians are over-matched, but they've mounted a ferocious defense that has led to Russian forces being unable to capture key cities like Kyiv and Kharkiv. Another throwback to World War II is the supply line issue. Like the Germans coming out of the Ardennes in 1945 during the Battle of the Bulge, Russian tanks are running out of gas. Ukrainians are using Javelin anti-tank systems with lethal precision. Countless videos of Russian convoys being bombed to bits. Almost everyone thought that Kyiv would be in Russian hands. It's not. The slow pace of this Russian invasion is now angering the neo-tsar in Moscow.
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Wait, should the Russians have acquired air superiority? Yes, they should have, as their air force is eons ahead of the Ukrainians, but apparently, they hit old air defense sites (via NYT):
For the Russian military, the difficult part came quickly.
On the first day of President Vladimir V. Putin’s invasion of Ukraine, his generals and troops followed a textbook strategy for land invasions. They attacked the country’s military installations and air defense systems with missiles launched from the air, sea and land, seeking to take ownership of the skies, and sped forces to Kyiv, the capital, with the goal of decapitating the government of the democratically elected president, Volodymyr Zelensky.
But then, things slowed. It is one thing to cross the border of another country with tanks and artillery, protected by warplanes above, Pentagon officials and analysts say. It is another thing entirely to lay siege to cities and an army populated by people willing to put their lives on the line to protect what they view as their sovereign right to self-determination.
Within a day of entering Ukraine, Russian forces lost some momentum, senior American and British officials said, as Ukrainian fighters mounted a resistance. No population centers had been taken, a senior Defense Department official told reporters at the Pentagon on Friday. Nor had Russia yet managed to achieve air superiority over Ukraine, partly because the Ukrainians are using mobile systems and partly because Russian missiles have hit old air defense sites, which could show a flaw in Russia’s intelligence. The Ukrainian air defense and missile defense systems were degraded, he said, but the country’s air force was still flying planes and denying air access to Russia.
Now, apparently, only a third of the Russian invasion force has been deployed, but that could change. Also, there must be an ammunition issue arising among Ukrainian defenders. They only have so many SAM missiles in these mobile defensive systems. They only have so many Javelins. Still, the fact they're holding has yielded dividends. The European Union is going to flood the country with $500 million in arms. The longer they hold out, the better chance of those arms being distributed. You all know the game. Meanwhile, this Russian invasion is getting bogged down by the land, the people, and some very bad intelligence. History has repeated itself for the moment.