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Vladimir Putin says he is a religious man, a great supporter of the Russian Orthodox Church. If so, he may well go to bed each night, say his prayers, and ask God: "Why didn't you put mountains in eastern Ukraine?"

If God had built mountains in eastern Ukraine, then the great expanse of flatland that is the European Plain would not have been such inviting territory for the invaders who have attacked Russia from there repeatedly through history. As things stand, Putin, like Russian leaders before him, likely feels he has no choice but to at least try to control the flatlands to Russia's west. So it is with landscapes around the world-their physical features imprison political leaders, constraining their choices and room for maneuver. These rules of geography are especially clear in Russia, where power is hard to defend, and where for centuries leaders have compensated by pushing outward.

Western leaders seem to have difficulty deciphering Putin's motives, especially when it comes to his actions in Ukraine and Syria; Russia's current leader has been described in terms that evoke Winston Churchill's famous 1939 observation that Russia "is a riddle wrapped in a mystery inside of an enigma." But it's helpful to look at Putin's military interventions abroad in the context of Russian leaders' longstanding attempts to deal with geography. What if Putin's motives aren't so mysterious after all? What if you can read them clearly on a map?

For Russia, the world's largest country by landmass, which bestrides Europe and Asia and encompasses forests, lakes, rivers, frozen steppes, and mountains, the problems come by land as well as by sea. In the past 500 years, Russia has been invaded several times from the west. The Poles came across the European Plain in 1605, followed by the Swedes under Charles XII in 1707, the French under Napoleon in 1812, and the Germans-twice, in both world wars, in 1914 and 1941. In Poland, the plain is only 300 miles wide-from the Baltic Sea in the north to the Carpathian Mountains in the south-but after that point it stretches to a width of about 2,000 miles near the Russian border, and from there, it offers a flat route straight to Moscow. Thus Russia's repeated attempts to occupy Poland throughout history; the country represents a relatively narrow corridor into which Russia could drive its armed forces to block an enemy advance toward its own border, which, being wider, is much harder to defend.

On the other hand, Russia's vastness has also protected it; by the time an army approaches Moscow, it already has unsustainably long supply lines, which become increasingly difficult to protect as they extend across Russian territory. Napoleon made this mistake in 1812, and Hitler repeated it in 1941.
Early Russia was indefensible. There were no mountains, no deserts, and few rivers.
Just as strategically important-and just as significant to the calculations of Russia's leaders throughout history-has been the country's historical lack of its own warm-water port with direct access to the oceans. Many of the country's ports on the Arctic freeze for several months each year. Vladivostok, the largest Russian port on the Pacific Ocean, is enclosed by the Sea of Japan, which is dominated by the Japanese. This does not just halt the flow of trade into and out of Russia; it prevents the Russian fleet from operating as a global power, as it does not have year-round access to the world's most important sea-lanes.

Russia as a concept dates back to the ninth century and a loose federation of East Slavic tribes known as Kievan Rus, which was based in Kiev and other towns along the Dnieper River, in what is now Ukraine. The Mongols, expanding their empire, continually attacked the region from the south and east, eventually overrunning it in the 13th century. The fledgling Russia then relocated northeast in and around the city of Moscow. This early Russia, known as the Grand Principality of Moscow, was indefensible. There were no mountains, no deserts, and few rivers.

Enter Ivan the Terrible, the first tsar. He put into practice the concept of attack as defense-consolidating one's position at home and then moving outward. Russia had begun a moderate expansion under Ivan's grandfather, but Ivan accelerated it after he came to power in the 16th century. He extended his territory east to the Ural Mountains, south to the Caspian Sea, and north toward the Arctic Circle. Russia gained access to the Caspian, and later the Black Sea, thus taking advantage of the Caucasus Mountains as a partial barrier between itself and the Mongols. Ivan built a military base in Chechnya to deter any would-be attacker, be they the Mongol Golden Horde, the Ottoman Empire, or the Persians.

Now the Russians had a partial buffer zone and a hinterland-somewhere to fall back to in the case of invasion. No one was going to attack them in force from the Arctic Sea, nor fight their way over the Urals to get to them. Their land was becoming what's now known as Russia, and to invade it from the south or southeast you would have to have a huge army and a very long supply line, and you would have to fight your way past defensive positions.
As long as a pro-Russian government held sway in Kiev, Russia's buffer zone would remain intact and guard the European Plain.
In the 18th century, Russia, under Peter the Great-who founded the Russian Empire in 1721-and then Empress Catherine the Great, expanded the empire westward, occupying Ukraine and reaching the Carpathian Mountains. It took over most of what we now know as Lithuania, Latvia, and Estonia-from which it could defend against attacks from the Baltic Sea. Now there was a huge ring around Moscow; starting at the Arctic, it came down through the Baltic region, across Ukraine, to the Carpathians, the Black Sea, the Caucasus, and the Caspian, swinging back around to the Urals, which stretched up to the Arctic Circle.

At the end of World War II in 1945, the Russians occupied territory conquered from Germany in Central and Eastern Europe, some of which then became part of the U.S.S.R., as it began to resemble the old Russian Empire writ large. This time, though, it wasn't the Mongols at the gates; after 1949, it was NATO. The fall of the U.S.S.R. in 1991 caused Russian territory to shrink again, with its European borders ending at Estonia, Latvia, Belarus, Ukraine, Georgia, and Azerbaijan, even while NATO crept steadily closer as it incorporated more countries in Eastern Europe.

Russia's Changing Borders

Two of Russia's chief preoccupations-its vulnerability on land and its lack of access to warm-water ports-came together in Ukraine in 2014. As long as a pro-Russian government held sway in the Ukrainian capital of Kiev, Russia could be confident that its buffer zone would remain intact and guard the European Plain. Even a neutral Ukraine, which would promise not to join the European Union or NATO and would uphold the lease Russia had on the warm-water port at Sevastopol in Crimea, would be acceptable. But when protests in Ukraine brought down the pro-Russia government of Viktor Yanukovych and a new, more pro-Western government came to power, Putin had a choice. He could have respected the territorial integrity of Ukraine, or he could have done what Russian leaders have done for centuries with the bad geographic cards they were dealt. He chose his own kind of attack as defense, annexing Crimea to ensure Russia's access to its only proper warm-water port, and moving to prevent NATO from creeping even closer to Russia's border.

What if Putin's motives aren't so mysterious after all? What if you can read them clearly on a map?
The same geographic preoccupations are visible now in Russia's intervention in Syria on behalf of Putin's ally, Bashar al-Assad. The Russians have a naval base in the port city of Tartus on Syria's Mediterranean coast. If Assad falls, Syria's new rulers may kick them out. Putin clearly believes the risk of confronting NATO members in another geographic sphere is worth it.

Russia has not finished with Ukraine yet, nor Syria. From the Grand Principality of Moscow, through Peter the Great, Stalin, and now Putin, each Russian leader has been confronted by the same problems. It doesn't matter if the ideology of those in control is czarist, communist, or crony capitalist-the ports still freeze, and the European Plain is still flat.
This article has been adapted from Tim Marshall's new book, Prisoners of Geography: Ten Maps That Explain Everything About the World.

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Vladimir Putin says he is a religious man, a great supporter of the Russian Orthodox Church. If so, he may well go to bed each night, say his prayers, and ask God: "Why didn't you put mountains in eastern Ukraine?"

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Mariupol has become the most heavily bombed and damaged city in Ukraine's war with Russia - having suffered the brunt of sustained Russian attacks. It is key to Moscow's military campaign in Ukraine. But why?

There are four main reasons why taking the port city would be such a strategic win for Russia - and a major blow for Ukraine.

Geographically, the city of Mariupol occupies only a tiny area on the map but it now stands obstinately in the way of Russian forces who have burst out of the Crimean peninsula.

They are pushing north-east to try to link up with their comrades and Ukrainian-separatist allies in the Donbas region of eastern Ukraine.

General Sir Richard Barrons - former commander of UK Joint Forces Command - says capturing Mariupol is vital to Russia's war effort.

"When the Russians feel they have successfully concluded that battle, they will have completed a land bridge from Russia to Crimea and they will see this as a major strategic success."

If Mariupol was seized, Russia would also end up with full control of more than 80% of Ukraine's Black Sea coastline - cutting-off its maritime trade and further isolating it from the world.

By holding out against advancing forces for the past three weeks, the defending Ukrainians have managed to preoccupy a large number of Russian troops. But that failure by Russia to secure a rapid capture of the city, has prompted Russian commanders to resort to a 21st Century version of mediaeval siege tactics.

They have pummelled Mariupol with artillery, rockets and missiles - damaging or destroying over 90% of the city. They have also cut off access to electricity, heating, fresh water, food and medical supplies - creating a man-made humanitarian catastrophe which Moscow now blames on Ukraine for refusing to surrender by an 05:00 deadline on Monday. A Ukrainian MP has accused Russia of "trying to starve Mariupol into surrender".

Ukraine has vowed to defend the city down to the last soldier. It may well come to that. Russian troops are slowly pushing into the centre and, in the absence of any kind of workable peace deal, Russia is now likely to intensify its bombardment - drawing little if any distinction between its armed defenders and the beleaguered civilian population which still numbers over 200,000.

If, and when, Russia takes full control of Mariupol this will free up close to 6,000 of its troops - organised into 1,000-strong battalion tactical groups - to then go and reinforce other Russian fronts around Ukraine.

There are a number of possibilities as to where they could be redeployed:

to the north-east to join the battle to encircle and destroy Ukraine's regular armed forces fighting pro-Kremlin separatists in the Donbas region

to the west to push towards Odesa, which would be Ukraine's last remaining major outlet to the Black Sea

to the north-west towards the city of Dnipro

2. Strangling Ukraine's economy

Mariupol has long-been a strategically important port on the Sea of Azov, part of the Black Sea.

With its deep berths, it is the biggest port in the Azov Sea region and home to a major iron and steel works. In normal times, Mariupol is a key export hub for Ukraine's steel, coal and corn going to customers in the Middle East and beyond.

For eight years now, since Moscow's illegal annexation of Crimea in 2014, the city has been sandwiched uncomfortably between Russian forces on that peninsula and the pro-Kremlin separatists in the breakaway self-declared republics of Donetsk and Luhansk.

Losing Mariupol would be a major blow to what is left of Ukraine's economy.

3. Propaganda opportunity

Mariupol is home to a Ukrainian militia unit called the Azov Brigade, named after the Sea of Azov which links Mariupol to the rest of the Black Sea. The Azov Brigade contains far-right extremists, historically including neo-Nazis.

Although they form only the tiniest fraction of Ukraine's fighting forces, this has been a useful propaganda tool for Moscow, giving it a pretext for telling Russia's population that the young men it has sent to fight in Ukraine are there to rid their neighbour of neo-Nazis.

If Russia manages to capture alive significant numbers of Azov Brigade fighters it is likely they will be paraded on Russian state-controlled media as part of the ongoing information war to discredit Ukraine and its government.

4. Major morale boost

The capture of Mariupol by Russia, if it happens, will be psychologically significant for both sides in this war.

A Russian victory in Mariupol would enable the Kremlin to show its population - through state-controlled media - that Russia was achieving its aims and making progress.

For President Putin, for whom this war appears to be personal, there is a historical significance to all this. He sees Ukraine's Black Sea coastline as belonging to something called Novorossiya (New Russia) - Russian lands that date back to the 18th Century empire.

Putin wants to revive that concept, "rescuing Russians from the tyranny of a pro-western government in Kyiv" as he sees it. Mariupol currently stands in the way of him achieving that aim.

But to Ukrainians, the loss of Mariupol would be a major blow - not just militarily and economically - but also to the minds of the men and women fighting on the ground, defending their country. Mariupol would be the first major city to fall to the Russians after Kherson, a strategically much less important city that was barely defended.

There is another morale aspect here and that is of deterrence.

Mariupol has put up fierce resistance - but look at the cost. The city is decimated, it lies largely in ruins. It will go down in history alongside Grozny and Aleppo, places that Russia eventually bombed and shelled into submission, reducing them to rubble. The message to other Ukrainian cities is stark - if you choose to resist like Mariupol did then you can expect the same fate.

"The Russians couldn't walk into Mariupol," says Gen Sir Richard Barrons, "they couldn't drive in with their tanks, so they've pounded it to rubble. And that's what we should expect to see anywhere else that really matters to them."

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Mariupol: Why Mariupol is so important to Russia's plan

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Mariupol has become the most heavily bombed and damaged city in Ukraine's war with Russia - having suffered the brunt of sustained Russian attacks. It is key to Moscow's military campaign in Ukraine. But why? There are four main reasons why taking the port city would be such a strategic win for Russia - and a major blow for Ukraine.

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Ukraine has made the headlines due to the ongoing tensions with Russia. In this map infographic, we examine Ukraine from a structural point of view.