Moscow is challenging Washington’s alliance with South Korea with a new security agreement with North Korea that deepens the historic division between the two Koreas. 

Messrs. Putin and Kim are to sign “a comprehensive security partnership treaty” at Pyongyang on Wednesday that replaces their longstanding “treaty of friendship and neighborly cooperation.”

The new treaty marks a major escalation of North Korea’s close ties with Russia that began with Mr. Kim’s visit to the Russian far east last September in which he met Mr. Putin at the Vostochny cosmodrome near the Amur River. 

Ever since, North Korea has been shipping artillery shells and other armaments to Russia while the Russians provide technological assistance in North Korea’s drive to put a satellite into space that’s capable of providing more than stock shots. 

Mr. Kim greeted Mr. Putin, on his first visit to North Korea in 24 years while the North’s party newspaper Rodong Sinmun  lavished effusive praise for the Russian leader and Russian-North Korean friendship —  alarming Seoul and Washington as North-South Korean relations plunge to their lowest level in recent years.

“Our people warmly welcome President Putin, who comes with the friendly spirit of the brave and just Russian people,” rhapsodized Rodong Sinmun.  “The deep-rooted and cooperative relationship between North Korea and Russia is reaching a new heyday”while “contacts and cooperation between the two countries are strengthened day by day.” 

The editorial was bereft of details, but Mr. Putin left no doubt of the significance of a trip that he clearly hopes will reshape the balance of power in Northeast Asia.

The Russian news agency Tass reported Mr. Putin telling Rodong Sinmun that Russia and North Korea “are ready to closely work together to bring more democracy and stability in international relations.” 

More specifically, Tass indicated that Russia would circumvent UN sanctions on dealing with North Korea — and get  around blockades in the international trading system that might inhibit relationships.

“To do this,”  Mr. Putin was quoted as saying, “we will develop alternative trade and mutual settlements mechanisms not controlled by the West, jointly oppose illegitimate unilateral restrictions, and shape the architecture of equal and indivisible security in Eurasia.”

Significantly, Mr. Putin expressed gratitude for North Korea’s “unwavering support for Russia’s special military operations in Ukraine, their solidarity with us on key international matters and willingness to defend our common priorities and views within the United Nations.” 

Not surprisingly, Washington views Mr. Putin’s visit to North Korea with the deepest suspicion.  The White House security and communications adviser, John Kirby, cited the impact of “the deepening relationship” between Russia and North Korea “on the Ukrainian people” as North Korean ballistic missiles hit Ukrainian targets — and the implications for “security on the Korean peninsula.”

As if to dramatize these concerns, South Korea’s military command is reporting North Korean construction along the demilitarized zone. For the second time this month, South Korean forces fired warning shots against North Korean soldier-workers who had strayed across the line. They turned back, but the implication was that hostilities could break out any time.

Tensions have escalated this month after South Korea’s conservative president, Yoon Suk-yeol, broke off an agreement reached under his left-leaning predecessor, Moon Jae-in, barring patrols along the DMZ. North Korea had consistently ignored the deal. 

How far will Russian largesse extend beyond words and vague promises, though? Radio Free Asia, which broadcasts from Washington, reported “the biggest issue” was whether Mr. Putin “will agree to provide advanced nuclear and missile technology.”

RFA reported a former White House coordinator arms control, Gary Samore, predicting North Korea “likely to request military support from Russia, including advanced air defense systems, aircraft, missiles, satellite technology, and submarine technology” — a shopping list paid for by North Korea’s unceasing shipments of artillery shells and missiles to Russia.