Russian President Vladimir Putin loves to play Russian roulette. Seeking to expand Moscow’s global influence, he continually places geopolitical bets, hoping they will pay off. While the world is currently watching the large number of chips he has placed on Ukraine, he also has wagers riding in other parts of Europe, the Middle East, Central Asia and Latin America.

But perhaps his most troubling side bet is in Africa. While Russia may not be able to act as a great power there, it has enormous potential to be deeply destabilizing—especially in the Sahal.

Over the last few years, this region of western and north-central Africa has been battered by jihadist insurrections, Chinese meddling and political instability. In almost every case, Mr. Putin had a hand in making bad situations worse.

For instance, last May, a military coup in Mali brought to power Col. Assimi Goita. In January another coup occurred in Burkina Faso, where Lt. Col. Paul-Henri Sandaogo Damiba overthrew the President Roch Kabore. Many of the officers involved in the coup had received training in Russia.

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There is more. Last December, several Western countries accused Mr. Goita of welcoming the arrival of Russian mercenaries (with the Wagner Group) from Eastern Libya. Mali denies the presence of mercenaries, but at the beginning of January, the Malian army announced that Russian troops have deployed to Timbuktu to train Malian forces.

It should also be noted that, following the sanctions that the Economic Community of West African States has recently imposed on Mali, protests have broken out against France in the African country.

A similar situation is taking place in Burkina Faso, where several pro-coup protesters waved Russian flags, chanting anti-French slogans. Moreover, according to The Daily Beast, it appears that then-President Kabore had rejected Damiba’s proposal in early January to hire Wagner Group’s Russian mercenaries, in order to fight jihadist militiamen.

This in itself does not prove that Russia orchestrated the coup, but it certainly confirms Damiba’s political closeness to Moscow. This is why, instead of firmly condemning the Burkina Faso coup, Moscow has expressed only generic “concern.”

Where might Mr. Putin choose to make his next African bet? The smart money is on Nigeria. Moscow and Abuja signed a military cooperation agreement last August.

All this activity raises two questions. The first is: How is Mr. Putin getting away with this?

Several factors combine to give him an unusually free hand. Beijing looks on smiling, because Putin’s moves jibe with Beijing’s expansive vision of pushing the West out of Africa. There is widespread discontent among the region’s populace. They are also upset over the lack of progress in the fight against jihadism and place much of the blame on France. As a result, France is becoming increasingly unpopular and its position increasingly weak in this area.

The Malian government recently denounced an alleged violation of its airspace by a French warplane and called for a review of its 2013 bilateral defense agreement with Paris in 2013. Bamako also called for the expulsion from the Sahel of 100 Danish soldiers who are part of the European Takuba Task Force. That task force is mainly promoted by Paris.

All of this is deeply concerning to the European Union, which fears being caught between the jihadist insurrection and Moscow’s growing political-military influence. Mr. Putin has also hit on the ideal instrument for expanding his political influence in Africa: Russian mercenaries. They have already worked a treat for him in the Central African Republic.

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The second question: Why is Mr. Putin doing this?

A stronger influence in the Sahel would give the Kremlin two complementary advantages: a stronger political network at the United Nations and a geopolitically weaker Western Europe. From this point of view, it is worth remembering that the Sahel is a crucial conduit of migratory flows that reach the EU from the south via Libya. Moscow likely aims to control those flows, which can be used to pressure Brussels. The recent Belarusian migration crisis shows how Russia is using this tactic to divide and intimidate the EU.

Mr. Putin’s moves in Africa should concern the transatlantic community. Europeans should worry that Moscow can use its influence in Africa to threaten their security. Americans should worry that Mr. Putin’s advances will aid China’s long-term goal of building up sufficient influence in Latin America and Africa to make the transatlantic a competitive space where the U.S. will have difficulty securing its own interests.

The U.S. and Europe should work more aggressively to counter Russian meddling in the Sahel. If they fail to do so now, things will only get worse.