Watching events in Ukraine, you might wonder if the Cold War is coming back. Russia annexed Crimea, now some of the eastern parts of Ukraine appear to be shifting into the Russian orbit, and looking into the future, it doesn't take much imagination to picture all of Ukraine dominated by Russia. There is palpable fear in some former Soviet republics and the memory of that dark and dangerous time has sent a chill through European capitals.

Is the Cold War coming back? That's what a number of commentators think, and that has led to the re-emergence (in their minds) of the weapon that kept us safe during the Cold War: nuclear weapons.

Ukraine, according to them, is proof that nuclear weapons are essential for safety. After the breakup of the Soviet Union there were a number of nuclear missiles on Ukraine's territory. The Ukrainian government eventually allowed the Russians to move those weapons back to their own territory in return for promises. Now commentators are saying that Ukrainians were foolish to let "idealists" talk them into giving up the one weapon that could have kept them safe.

It's comforting to think about things in familiar terms. But new evidence suggests the ideas developed during the Cold War about nuclear weapons were wrong. In retrospect, they appear to be more dangerous, clumsier, and less politically useful than most people believed at the time.

Much of this re-evaluation is based on new evidence about events between 1945 and 1989. But, ironically, some of the best evidence comes from events in Ukraine.

Imagine that Ukraine had kept some nuclear weapons or developed a small nuclear arsenal after independence. Could such an arsenal keep them safe? Imagine yourself at the table last February when discussions were taking place about what to do. Russian troops are infiltrating into Crimea (with their insignia removed) and encouraging political unrest and separatist sentiment. You are one of the leaders of a nuclear-armed Ukraine. What are your options?

Well, you could drop nuclear weapons on the infiltrating troops. Of course, those weapons would kill thousands or even tens if thousands of Ukrainian civilians along with the Russian troops. And radiation from those blasts could blow far and wide over Ukraine (or Russia, or even Europe for that matter).

You could drop nuclear weapons on the Russian troops still inside Russia near the Ukrainian border. But again, the radiation might blow back on your own country and kill your own citizens. And the Russians might be tempted, once the war had become a nuclear conflict, to use nuclear weapons against your cities.

Finally, you could threaten to use your weapons against Russian cities. You could even, in the last resort, use them. But the destruction of Russian cities does you little good. It would do nothing to stop the Russian troops drawn up at your border from overrunning your country and meting out harsh retribution to your citizens.

The ability to destroy your adversary's cities is not really a very useful one. War is about armies -- about military forces. There were enough cities destroyed on both sides in World War II to prove that destroying cities doesn't lead to surrender. What you want is not a weapon that can destroy a city in one blow, but a weapon that can cleanly and selectively destroy military forces.

But wouldn't the weapons have prevented Russia's president, Vladimir Putin, from ordering troops into Ukraine in the first place? Perhaps. If he was afraid. But Stalin himself once said that, "The nuclear weapon is something with which you frighten people with weak nerves." Does Putin seem easily frightened? There is almost nothing useful you can do with nuclear weapons against unmarked troops infiltrating territory.

We don't often think about it, but nuclear weapons have severe limitations. They are so large and clumsy that there are hardly any circumstances in which they are really the best tool for the job. This is a case of awe obscuring utility. We get so caught up in the awesomeness of nuclear weapons, we forget to notice that they are hardly useful at all.

If the biggest tool were always the most useful, workmen wouldn't ask their assistants if they'd brought the right tool for the job. They'd say, "Well, did you bring the biggest tool for the job?"

The trend in warfare is away from bigness and toward precision. Think about the weapons that have been most useful in the U.S. arsenal over the last 40 years: smart bombs, drones, cruise missiles -- highly accurate, small weapons have been a mainstay of the U.S. military in a series of wars. And as the bombing campaign against Serbia, and the the two campaigns against Iraq, and the war in Afghanistan (among others) have shown, precision weapons are highly useful. Nuclear weapons have sat unused in their silos.

The future looks increasingly like it will be dominated by tiny weapons with extreme sensors or cameras that can be used surgically. Clumsy, blundering, bull-in-a-china-shop weapons like nuclear weapons increasingly seem like evolutionary dead ends: dinosaurs from a distant past.

Are we headed into a new Cold War? Probably not. We are likely heading into a time of greater conflict with Russia and potentially dangerous confrontation with China. Will the measures and attitudes of the Cold War serve as a guide to keeping our country safe? Unlikely.

The events in Ukraine are a warning shot across our bow. The commentators who say those events prove that nuclear weapons are the answer have not thought carefully about the military realities we face today. Locked in a mindset from a past that will never come again, the course they have laid out is not a safe and secure one for our future.

Ward Wilson is a Senior Fellow at BASIC, a security policy think tank in Washington and London, and the author of Five Myths About Nuclear Weapons, published by Houghton Mifflin Harcourt.