“Someone to talk to.”

That is how McGeorge Bundy, President John F. Kennedy’s national security adviser, described the Anglo-American alliance. The “Special Relationship,” the exceptionally close collaboration forged during the most desperate days of the Second World War, has proven remarkably durable.

By contrast, relations between France and the United States have often proven extremely difficult and challenging. This was especially the case during the Kennedy administration, when Washington’s promotion of an increasingly integrated Atlantic alliance collided directly with the extreme independent nationalism of France’s imperious President Charles de Gaulle. Contrasting sometimes conflicting worldviews have continued to characterize our two nations.

“Brexit,” the lengthy, complex, sometimes tortured divorce of Britain from the European Union, following the surprise result of a 2016 referendum, left painful scars in that nation’s relations with the rest of Europe.

In this context, the Anglo-French agreement July 11 to develop close cooperation in nuclear weapons strategy assumes considerable importance. The accord was the capstone of the three-day visit of President Emmanuel Macron of France to Britain.

The bilateral security agreement simultaneously reflects both the direct threat of wider European war as a result of Russia’s continuing costly invasion of Ukraine, and insecurity across the board about the reliability of the United States as an ally during the unpredictable second term of President Donald Trump.

The nuclear dimension from the start of the atomic age defined in important ways U.S. relations with other nations, especially principal allies.

From the beginning of the Manhattan Project to develop an atomic bomb, Britain along with Canada was a close partner of the United States. The three governments, working under great pressure, devoted unprecedented resources to create the terrifying weapon used with terrible effect decisively to end the war with Imperial Japan in August 1945.

The Truman administration made sincere, ultimately frustrated efforts to bring atomic weapons under the supervision of the United Nations. The successor Eisenhower administration did lead the complicated diplomacy that resulted in creation of the International Atomic Energy Agency, which has been generally effective in encouraging civilian use of nuclear power and restraining pressures for nuclear weapons proliferation.

In 1958, amendment of the McMahon Act updated the special partnership with Britain in the nuclear weapons sphere. Nuclear military technology was shared with the British, and the U.S. played an active role in supplying a credible nuclear deterrent to the close ally.

Dependency inevitably led to tensions. During the Kennedy administration, the abrupt cancellation of the Skybolt bomber program completely upended Britain’s force planning. Kennedy officials scrambled to provide the new Polaris nuclear-armed submarine as a substitute. The collaboration continues with today’s Trident submarine force.

Relations with France during the Second World War as well as the Cold War provide a dramatic contrast. De Gaulle, leader of Free French forces during the war, proved demanding and rigid in the extreme.

Perhaps that style was inevitable, given the humiliation of France’s stunning, devastating defeat by Germany’s military in 1940.

Both President Franklin D. Roosevelt and Prime Minister Winston Churchill disliked the rigid, insecure, beleaguered French leader. Supreme Allied Commander Gen. Dwight Eisenhower did have good rapport with him.

When de Gaulle became president of France in 1958, he quickly emphasized a French nuclear military force to achieve desperately needed national prestige. France withdrew from NATO in 1966.

Compared with this history, recent years have been relatively stable among NATO nations. In 2009, France returned to NATO.

Beyond but related to this specific bilateral agreement, the NATO alliance has been considerably strengthened by Russia’s overt military invasion of Ukraine in 2022, and earlier annexation of territory. The alliance last year celebrated the 75th anniversary.

The new accord strengthens Europe’s security whatever the temperature in Washington.

Arthur I. Cyr is author of “After the Cold War.”