The Republican presidential candidates hold their hands over their hearts during the singing of "The Star-Spangled Banner" before Tuesday night's debate in Las Vegas. (Mike Nelson/European Pressphoto Agency)

The fifth round of the Republican debates hinged on questions of national security and foreign policy. There were real divisions between some of the leading candidates on the main stage, who sparred over how best to protect the nation, defeat the Islamic State and settle the brutal, destabilizing Syrian civil war.

But many made rather bewildering claims about the Middle East and the strategy needed to deal with its crises.

[As the Republicans debate, remember these simple truths about Muslims]

Sen. Ted Cruz (Tex.) repeated his insistence that the United States "carpet bomb" the Islamic State, a militant group that controls significant territory in Iraq and Syria.

"What it means is using overwhelming air power to utterly and completely destroy ISIS," said Cruz, using another term for the group. When pressed on the matter by CNN's Wolf Blitzer, who asked whether cities full of civilians were fair game, Cruz offered this strange dodge.

"You would carpet bomb where ISIS is, not a city, but the location of the troops.… But the object isn't to level a city. The object is to kill the ISIS terrorists," he said.

The problem with airstrikes against the Islamic State, though, is that its fighters do operate in areas teeming with civilians. The Islamic State built its strongholds in major cities such as Raqqa (in Syria) and Mosul (in Iraq). It took advantage of political disorder and the unraveling of these states and surged in to fill a vacuum.

Cruz's emphasis is on tough, withering, relentless action, but you can't bomb the Islamic State to smithereens without contemplating an enormous civilian death toll. That places Cruz in the same camp as Syrian President Bashar al-Assad, who for years has been bombing civilian areas in his own country with barrel bombs and other crude, indiscriminate forms of munitions.

[The Republican obsession with "radical Islam" is a smokescreen for something else]

Moreover, as The Post's Fact Checker points out, carpet bombing is not something the United States has done in a very long time. Cruz held up the heavy bombardments of the 1991 Gulf War as a counterpoint to the Obama administration's current strategy, but carpet bombing was never part of the program then, either.

Cruz and, to varying extents, other candidates onstage appeared to view the Middle East as a kind of set for "American Sniper" — a woebegone place of dusty towns crawling with bad guys and not much else.

What else can explain the willingness to entertain such civilian casualties? What else can explain the rather strange talking point from Donald Trump, the current front-runner, that the United States should simply "take the oil" lying around in Iraq and Syria?

Judging from the debate, these countries are not sovereign nations with complex societies and failing governments but rather springboards for a dangerous and all-encompassing "caliphate." It's a worldview the jihadists themselves espouse. (Trump, to his credit, did acknowledge that precipitating a lot of the current crises with the 2003 U.S.-led invasion of Iraq was perhaps a bad idea.)

Ben Carson, the retired neurosurgeon, had his own quixotic attempt at policymaking when talking about what to do with Syrian refugees. Fresh from a trip to a refugee camp in Jordan, Carson made the salient point that most refugees don't want to leave their homes but are forced to by the circumstances of war.

But he then went down yet another rambling path to justify Republican opposition to resettling Syrian refugees in the United States. Carson suggested that refugees, with no attention paid to their background or city of origin, be moved to Hasakah province in northeast Syria — "an area that's as big as Lebanon," as Carson observed.

[Ben Carson's remarkable gibberish on Syria and Iraq]

"It's controlled by the Kurds, the Christians and the moderate Sunnis. And there are airstrips and hotels. You could settle a lot of people there," he said.

This is not a serious proposal, not least because Hasakah is still a theater of war and the site of clashes between Kurdish militias and the Islamic State.

Beyond that, Carson and others onstage invoked as an article of faith the necessity to fully ally with the Syrian Kurds. These include one faction that is affiliated with an organization still on the State Department's list of terrorist groups. Rights groups have also pointed the finger at Syrian Kurdish militias, accusing them of carrying out war crimes in non-Kurdish areas of northern Syria.

There is a substantive conversation to be had about the geopolitical benefits and costs of backing the region's various Kurdish parties and militias, not all of which have identical agendas and bases of support. Washington has to also weigh its relationship with a vital ally, Turkey, which is adamantly opposed to any solution that creates a de facto Kurdish state on the other side of the Syrian border.

But none of this was being deliberated in Las Vegas, of course.

Instead, there was a vague embrace of Sunni Arab elites — namely the ruling royals of countries such as Jordan and Saudi Arabia — and a parallel demonization of Iran, a regional bogeyman on the other side of a sectarian divide with the Saudis.

Sen. Marco Rubio (R-Fla.), one of the more polished speakers on foreign policy, lamented the nuclear deal cut with "the Shia in Iran," while others, including Govs. Chris Christie and John Kasich, warned of an expanding Iranian "empire" and the threat of "a Shia crescent" linking states and militant organizations in the Middle East.

Iran has real influence in Iraq and Syria — the former largely the consequence of the United States removing Iraqi dictator Saddam Hussein. But some of its putative threat is overblown. Iran, for example, is hardly "winning" in Yemen's civil conflict, as was suggested at the debate. Rather, Saudi Arabia, in its war against rebels loosely seen as Iranian proxies, has failed despite months of airstrikes and a blockade that has led to a humanitarian crisis in the impoverished country.

Nevertheless, a number of Republican candidates celebrated the recently announced Saudi-led Islamic military alliance, a coalition of nearly three dozen countries that does not include Iran and whose efficacy and capabilities remain very much in doubt.

Here are highlights from CNN's Republican presidential debate on Dec. 15 in less than two minutes. (Sarah Parnass/The Washington Post)

This rhetoric is far removed from the frustration that's increasingly being voiced in Europe, with many politicians there pointing to the dangerous radicalism incubated by the Saudi state, which sees itself at the vanguard of Sunni Islam.

"From Saudi Arabia, Wahhabi mosques all over the world are financed. Many Islamist threats come from those communities," said German Vice Chancellor Sigmar Gabriel last week, referring to the more orthodox strain of Sunni Islam propagated in Saudi Arabia.

In a debate about national security and the threat of "radical Islamic terror," that detail strangely never came up.

Related on WorldViews

As the Republicans debate, remember these simple truths about Muslims

The Republican obsession with "radical Islam" is a smokescreen for something else

Ben Carson's remarkable gibberish on Syria and Iraq

7 Middle East crises that are a bigger problem than Iran's nuclear program