There are sliding door moments in history when an ill-considered decision by government will have disastrous consequences that echo through the ages.
For example, following the Armistice with Germany in 1918, the signatories to the Versailles Treaty treated the defeated Germany harshly.
Twenty years later, the resentment of the German people was harnessed by Hitler to unleash the destruction and misery of World War II.
The allies did learn the lesson of Versailles in 1945 and, through America's Marshall Plan, helped rebuild a shattered Germany. It is now a reunited free enterprise democratic nation and the mainstay of the European Union.
When the Soviet Union collapsed in 1991, current Russian President Putin described it as: "the greatest geopolitical catastrophe of the 20th century".
At that time, the US and its allies could have followed the path of the Marshall Plan and helped the fledgling Russian democracy under President Yeltsin create a free enterprise economy from the wreckage of Soviet communism.
Instead, the US and its NATO (North Atlantic Treaty Organisation) allies pressed their economic and military advantage. Led by US President Bill Clinton in the 1990s, when the new Russia was at its weakest, the former communist eastern European Warsaw Pact countries, for example Poland, were invited into the European Union and the NATO defence system.
Suddenly Russia's old adversaries from Western Europe were on their doorstep.
Bill Clinton should have known better. As a graduate from Oxford University in PPE (philosophy, politics and economics) he would have learned Versailles's lessons. Still, he didn't heed them when he held the levers of world power.
So, 30 years later, it has come to this.
Russia has now drawn a line in the sand at the Ukraine border.
No further east.
Remember, Ukraine was the second-largest republic in the old Soviet Union. It wasn't a buffer state, but an integral part of the former USSR.
Since the fall of the Soviet Union, Ukraine has taken a different path from Russia. It is trying to build a democracy with mixed success. But what worries the autocratic Russian President Putin is that the Ukraine's current leadership is attracted to the idea of also joining the European Union and NATO. He desperately needs to keep Ukraine as a buffer between his forces and those of his adversaries.
That is why Putin has assembled 130,000 troops on his western borders and is carrying out "war games" in the region. He has made a list of demands on the west, seeking guarantees that they will stop the eastward expansion of their influence, and so improve Russian security.
Putin has gained no such assurances, but instead the threat of crippling trade sanctions if he invades Ukraine. As a result, the world now faces its most dangerous situation since the Cuban missile crisis in 1962.
What will happen next?
Will Putin seize control of Ukraine and absorb it into Russia?
Intelligence sources report that Russian plans are at an advanced stage to plant a "false flag" by staging an atrocity in Ukraine to justify an invasion to "protect" ethnic Russians. It's a move straight out of the Putin playbook.
Such a strategy is possible, but not likely. Putin plays a weak international hand exceptionally well. The Russian economy has shrunk to about the size of Australia's, but it still has considerable international clout with a powerful military and thousands of nuclear missile warheads.
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However, Putin realises that he cannot put back together the former Soviet Union. What may be possible is to restore Russian dominance of the republics of the former USSR, making them client states and allies.
To achieve this in Ukraine, Putin is more likely to continue his salami-slicing tactics of ongoing interference in Ukrainian affairs. There are millions of ethnic Russians in enclaves in Ukraine, particularly near the Russian border.
In 2014, guerrilla forces backed by Russian advisers and equipment took over part of this territory in the Donbas region, sponsoring an "independence" movement. Putin also took back into Russia the Crimean Peninsula on the Black Sea, while the world looked on and did nothing.
The worry is that this earlier success may embolden him in 2022, and Putin may overplay his hand with disastrous consequences for Europe.
However, his next move is more likely to install a puppet government in Kiev that will not listen to the siren song of the west; stay out of NATO and the European Union and restore a buffer zone for Russia.
If Putin can achieve this, the modern "tsar" will have gone some way to restoring Russian power extinguished in 1991.
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