It seems impossible to imagine the most impoverished, backward communist regime in Asia, run by a madman and recovering from a crippling famine, should set out to build a long-range missile that could deliver a nuclear weapon all the way to the United States. And yet Mao Zedong’s China did it.

In 1964, as today, Americans had trouble accepting the new reality of their vulnerability. United States officials were slow to realize that China was on the verge of testing a nuclear weapon that year, and later were surprised to learn that Beijing was not willing to settle for only short-range missiles that could strike neighbors like Japan. The scope of Mao’s ambition — to develop a thermonuclear weapon that could hit the United States — did not match American preconceptions of China. And so, collectively, we did not believe it.

Over the past few years, North Korea has made every possible effort to indicate that, like Mao’s China, it was committed to developing a nuclear-armed intercontinental range ballistic missile. Starting in 2014, North Korea began testing missiles at a much faster pace than before. Kim Jong-un, the country’s leader, began visiting defense industry plants all over the North, showing off newly built facilities and the new machine tools inside them. North Korea began releasing increasingly explicit pictures of its missile program, including some of new rocket engines and tests of the vehicle that would protect a nuclear weapon as it re-entered the atmosphere.