Republican presidential candidate Ben Carson might be a superb neurosurgeon, but how well that has prepared him for the White House was one of the questions tested in the first GOP debate.

Moderator Bret Baier of Fox News asked Carson whether he would have used military force against Syrian President Bashar al-Assad after there was convincing evidence that Syrian forces had used chemical weapons on its own people.

Carson didn’t answer the question directly. Rather, he said reductions in America’s military forces have curtailed its options. He segued from that into the charge that America’s stature on the world scene has suffered.

"Our friends can't trust us anymore," Carson said . "You know, Ukraine was a nuclear-armed state. They gave away their nuclear arms with the understanding that we would protect them. We won't even give them offensive weapons."

In this fact-check, we will look at whether Carson has his history straight. Was Ukraine a nuclear state? And did it give up its nukes with assurances that the United States would protect it?

The answer to the first question is: not really. As for promised protections, the signed documents tell us that America pledged not to attack Ukraine, and that’s quite different from a promise to defend it.

Ukraine, nuclear weapons and the end of the Soviet Union

The 1991 breakup of the Soviet Union generated enormous concern over the fate of the nuclear arsenal it had spread across three states that were newly independent -- Belarus, Kazakhstan and Ukraine -- as well as in Russia itself. During the first six months of 1992, Moscow was quick to retrieve all of its tactical, or short-range, nukes. Corralling the strategic weapons, such as intercontinental missiles and bomber-based warheads, was trickier.

Belarus and Kazakhstan agreed to dismantle or return what they had. But Ukraine looked at the roughly 1,900 warheads on its soil and began seeking something in exchange before it gave them up.

Brian Finlay, a specialist in nonproliferation at the Stimson Center, a military-focused think tank in Washington, told us there was actually never any question that Ukraine would eventually relinquish those weapons.

"They had announced that they would become a non-nuclear weapon state even before their declaration of independence," Finlay said. "Essentially, it was something that they traded off in order to encourage international recognition."

According to a report by Steven Pifer, the U.S. Ambassador to Ukraine between 1998 and 2000, Ukraine wanted Russia to promise to respect its sovereignty and its borders, a promise that Russia made but has since broken. But just as important, Ukraine wanted money. The highly-enriched uranium in the warheads was valuable, plus Ukraine wanted somebody else to cover the costs of dismantling the silos and other infrastructure. And Ukraine knew that going non-nuclear would open the door to better ties with the West.

Ukraine couldn’t launch a single missile

While Carson called Ukraine a nuclear-armed state, Matthew Bunn, a nuclear specialist at Harvard University’s Kennedy School, told PolitiFact that there’s a big difference between housing a bunch of warheads and being able to fire them.

"The Ukrainians did not, repeat not, ever have the ability to launch these weapons — which is what would have made them a nuclear power, as Carson claimed," Bunn said. "As you might imagine, command and control arrangements for intercontinental nuclear missiles are done very carefully, with an eye on security and making sure that nobody other than the authorized people can launch these things. There are codes and so on that are needed. Even when you’re the officer sitting in the launch control center, launching the thing can’t be done without relevant commands, unlock codes, etc. from above."

Bunn said the Ukrainians were trying to figure out how to gain control of the weapons, but they never did. The only way they could be used was if the governments in Moscow and Kiev agreed to do so.

Not only did Moscow hold the launch codes, but its troops had removed the firing systems on every warhead that was kept in storage in Ukraine.

The deal that de-nuked Ukraine

It took a series of agreements to finally clear the way for Ukraine to get rid of the weapons it held. Early in 1994, the United States agreed to provide money through the Nunn-Lugar program to dismantle Ukraine’s nuclear infrastructure. Russia agreed to write down the debts Ukraine owed. In December 1994, the United States, Russia, the United Kingdom and Ukraine signed the Budapest Memorandum of Security Assurances .

Pifer described in his report how Washington wanted security assurances that avoided creating broad guarantees.

"State Department lawyers thus took careful interest in the actual language, in order to keep the commitments of a political nature," Pifer wrote. "U.S. officials also continually used the term ‘assurances’ instead of ‘guarantees,’ as the latter implied a deeper, even legally-binding commitment of the kind that the United States extended to its NATO allies."

The agreement stated that the United States, the Russian Federation, and the United Kingdom reaffirm certain commitments:

To respect the independence and sovereignty and the existing borders of Ukraine.

To refrain from the threat or use of force against the territorial integrity or political independence of Ukraine

To seek immediate United Nations Security Council action to provide assistance to Ukraine, as a non-nuclear-weapon state party to the Treaty on the Nonproliferation of Nuclear Weapons, if Ukraine should become a victim of an act of aggression or an object of a threat of aggression in which nuclear weapons are used.

Pifer writes that American diplomats went so far as to make sure that the Russians and Ukrainians understood specifically that the English meaning of "assurance" was not the same as a "guarantee."

In short, the United States never promised to protect Ukraine. All it did was promise not to attack it.

Our ruling

Carson said Ukraine was a nuclear-armed state and that it gave up those arms with the understanding that the United States would protect it. While it is true that about 1,900 nuclear warheads were on Ukrainian soil, experts make it clear that Ukraine merely possessed the weapons and had no ability to use them.

Meanwhile, the security agreements struck after the fall of the USSR specifically avoided committing the United States to protecting Ukraine, instead committing not to attack the newly created independent nation.

We rate this claim False.