Protect the king. The first rule of chess is the basic principle of Western policy on Saudi Arabia. It was Canada's policy under the Conservatives, and it is Canada's de facto policy under the Liberals. The new government has no plans to stop a $15-billion weapons contract.

Let's be clear: These are weapons. The Canadian light armoured vehicles, or LAVs, that will be sold to Saudi Arabia are not jeeps. They are big, 8x8 armoured vehicles with gun turrets on top. And they are being sold to an internal security force, not Saudi Arabia's regular army. That force, the Saudi Arabian National Guard, is tasked with protecting the royal family. It deploys its armoured vehicles at protests. There can be no assurance they will never be used against Saudi civilians.

Of course, money and jobs are at stake: Prime Minister Justin Trudeau's new government does not want to cancel a massive contract for vehicles that would be built in London, Ont.

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But the contract also fits with Canadian policy toward Saudi Arabia under both the Conservatives and now effectively under the Liberals: backing the Saudi regime despite its poor human-rights record. That is U.S. policy, and it has been Canadian policy, too. Western countries fear that if the royal family ever fell, it would lead to something worse: Islamist jihadis, or chaos.

That was very much the policy of Stephen Harper's Conservatives. Yes, they liked the trade benefits of selling LAVs. But they were gung-ho about the foreign policy. They would support what one Conservative privately called a "stablish" Middle Eastern government that was reasonably friendly, and opposed to the country the Tories saw as the region's real bad guy, Iran. The LAV deal was made to protect the Saudi royal family. "I'd sign it again today," former foreign affairs minister John Baird told CBC News on Tuesday.

The Liberals are not gung-ho. But in practice, the policy is still to protect the king.

Foreign Affairs Minister Stéphane Dion condemned Saudi Arabia's execution of 47 people, including 43 al-Qaeda operatives and a prominent cleric, Sheik Nimr al-Nimr, who had been a voice for the country's Shia minority.

"We don't support what they do to their population when they violate human rights, but when there's progress, we underline it," Mr. Dion said in an interview with The Globe and Mail. Saudi Arabia has also been a security partner, helping co-ordinate countries against terrorism and organizing Syrian opposition forces, he said. But he insisted that allowing the sale of LAVs is not support for the Saudi regime.

"It's not a backing, it's simply a private-company contract," he said. The Saudi government has committed to not using the LAVs against civilian populations, he said. "If ever there was a breach of confidence, that would put future contracts in danger," Mr. Dion said.

But it is hard to accept such assurances as guarantees. The LAVs will not go to Saudi Arabia's regular army. They are for the Saudi Arabian National Guard, which is a parallel force tasked with protecting internal security as well as the royal family.

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The SANG was developed separately from the regular army, recruited from loyal tribes, answering to its own ministry, not the defence ministry. The regular army has tanks to fight foreign forces; the SANG has armoured vehicles to move quickly through cities. It already has Canadian LAVs bought in the 1990s.

"They've deployed their armoured vehicles within the Shia areas in the east, Qatif and al-Awamiyah in particular. And the purpose of that was to intimidate the Shia protesters," said Jacqueline Lopour, research associate at the Centre for International Governance Innovation. They were also deployed to Shia protests in neighbouring Bahrain in 2011.

What is more, the Saudi regime seems increasingly nervous. There are fears of Shia revolts, of Sunni extremists such as al-Qaeda and Islamic State, popular dissent, and royal family rivalries. Arab Spring dissent was quelled with rich benefits; now oil wealth is dipping.

Of course, there are conundrums. If Canada does not sell armoured vehicles to Saudi Arabia, someone will. Some countries are selective: Germany sold the Saudis patrol boats, but not tanks. The Liberal government is loathe to cancel a done deal. But there should be no doubt about the purpose of this sale: to protect the king.