We begin today’s respite with an easy, one-question pop quiz:

QUESTION: At the end of the 20th century’s Cold War, the three nations with the largest nuclear arsenals were: the United States, Russia, and –

(A) Britain, (B) France, (C) China, (D) none of the above?

And the correct answer, as you probably know, is: (D).

When the Soviet Union collapsed, about one-third of the former Soviet nuclear weapons were still in Ukraine, the suddenly untethered Soviet region just southwest of the rest of Russia. Ukraine had far more nukes than Britain, France and China. Well before the historic election in which more than 90 percent of Ukrainians voted to become an independent nation, Ukraine had instantly become the world’s third-ranked nuclear power.

Ukraine possessed 1,900 Soviet strategic nuclear warheads (but lacked operational control of them), according to the Washington-based Nuclear Threat Initiative’s historic analysis, and between 2,650 and 4,200 ex-Soviet tactical nuclear weapons. Two other regions outside Russia – Belarus and Kazakhstan – had smaller numbers of Soviet nuclear weapons.

In a far-sighted development, U.S. Sens. Sam Nunn, D-Ga., and Richard Lugar, R-Ind., drafted the historic Cooperative Threat Reduction Act, that financed programs to secure arsenals of weapons of mass destruction that were vulnerable to being obtained by terrorists around the world. The United States financed the program that enabled the flat-broke, newly noncommunist Russia to get those vulnerable nuclear weapons back to Russia, where they could be secured and safely destroyed. It remains the world’s noblest program never to win a Nobel Prize.

Ukraine’s leaders saw the nuclear weapons in what had suddenly become their arsenal as being a potentially powerful diplomatic and security bargaining boondoggle. They wanted to be accepted and respected by Europe and the West – not just militarily by NATO but economically by the European Union.

In 1994, in an agreement known as the Budapest Memorandums, signed by Russia, Ukraine, the United States and Britain, the signatories pledged they would respect Ukraine’s existing territorial borders and sovereignty. They also pledged that none of the signers would use force or threaten to use military or economic force against Ukraine.

Yet in 2014 and now, Russia’s President Vladimir Putin has ordered his military to mount military assaults against the sovereign and independent Ukraine that his predecessors recognized and vowed to respect. In 2014, Putin seized Crimea and militarily put it under Russian control. This week he has escalated his military assaults – and U.S. officials believe, cyberattacks against Ukraine banking – against Ukraine. And he has amassed what U.S. intelligence officials say is now 190,000 Russian troops surrounding Ukraine in what President Joe Biden believes will be an invasion of Ukraine that will target the capital, Kyiv.

Why? There are two primary reasons. One has long seemed uppermost in Putin’s mind: Putin has made clear that he believes Ukraine is not – and can never be! – an independent country. Putin considers Ukraine historically and forever Russian. Period. Thus, his mind seems to explode every time Ukraine leaders seek to join the European Union or even develop trade relationships with Europe. That was what caused him to explode and take Crimea by force in 2014.

A Putin invasion that takes Kyiv will be the most devastating military conquest Europe has seen since Adolph Hitler. It’s a valid comparison. A Putin invasion will shame all Russians, given the historic suffering their families endured in battling invading Nazis.

Putin also has a list of security concerns that come down to the true fact that, ever since the collapse of the Soviet Union, the United States has agreed (and, yes, even promoted) an eastward expansion of NATO. Former Soviet eastern bloc satellites are now NATO members. And Ukraine keeps saying it wants that too – prompting Putin to erupt every time, even though there’s no NATO interest in doing any such thing.

Here Putin has some valid concerns that have bipartisan roots that reach all the way to the USA. President George H. W. Bush’s Secretary of State James Baker once suggested to Soviet President Mikhail Gorbachev that maybe NATO would stay put and move “not one inch” toward Russia. President Bush was furious when he heard of Baker’s suggestion. But Gorbachev apparently considered it an assurance.

Enter President Bill Clinton. He swept aside objections from his top defense officials and surprised them, according to recently declassified documents, by pursuing a fast-track eastward expansion of NATO. But this was more than just reflex negativity from the Pentagon. For the architect of America’s Cold War policy, diplomat George Kennan, weighed in as well. In a 1997 New York Times commentary, the 93-year-old Kennan cautioned us all. “Expanding NATO,” Kennan wrote, “would be the most fateful error of American policy in the entire post-cold-war era.”

“The Most Fateful Error,” now playing on a news screen near you.

Martin Schram, an op-ed columnist for Tribune News Service, is a veteran Washington journalist, author and TV documentary executive. Readers may send him email at martin.schram@gmail.com