Shortly before the Six-Day War broke out, I attended an Israeli Defense Forces demonstration of military prowess at a site outside Tel Aviv. We foreign reporters were unimpressed as young Israeli recruits scrambled clumsily over the sand dues.

That was exactly what the Israelis intended. The show of ineptitude was part of the Israeli plan to generate over-confidence among Arab forces threatening Israel’s southern and eastern borders. The Israelis even sold a highly respected New York Times military analyst on the myth that their tanks were so decrepit that they had to be hauled into battle on semi-trailers. It turns out that was the fastest way to move them — fueled, stocked with ordnance and with fresh crews — from front to front.

Egypt, Syrian and Jordan would learn the truth on June 5 when the Israeli air force launched a pre-emptive strike against Egyptian and Syrian air bases and wiped out most of their planes on the ground. The IDF thereby gained air superiority which turned Egyptian tanks in the Sinai, Jordanian armor on the west bank, and Syrian forces on the Golan Heights into shooting gallery targets for Israeli fighter-bombers.

The thing I remember best about that earlier flailing pretense of weakness was the pacifist-sounding talks I heard from a young IDF lieutenant involved in the exercise. “Wars don’t solve anything,” he said to a group of reporters with some fervor. Maybe it was premonition. He was killed in the Sinai on the first day when an Egyptian rocket-propelled-grenade hit the half-track from which he was directing fire on Egyptian infantry.

It’s a bitter irony that he was both wrong and right. The war did resolve some important matters, such as whether Israel would survive as a nation state. Israel indeed survived and has strengthened its position in the half-century since. It now has a formal peace with Egypt, thanks to the 1976 Camp David Accords and a largely tacit understanding with Jordan, Saudi Arabia, Kuwait, and the Arab emirates that the main threat they all face is Iran.

He was right, though, in that the war that would kill him and those fought since would only further aggravate the personal hostility that separates Jews and Arabs living in the territory Israel now controls. I flew back to Israel on the fourth day of the war, landing in a blackout at Lod airport in a DC-10 piloted by the middle-aged managers of El-al, who had taken over from the younger pilots fighting the war. The few passengers, mostly reporters, cheered when they landed us safely.

On the way up to Jerusalem in a rented car next day, I gave a ride to four Israeli soldiers who were hitch-hiking, not unusual in an army noted for improvisation. I asked them if Israel was going to return the land they had just conquered. These were not the clumsy recruits the IDF had put on display weeks before, but tough, battle-hardened men with faces leathered by the desert sun. One, perhaps a Yemeni Jew, used an Arab word, sounding like “feesh,” in reply. Another, who spoke English, translated: “Nothing doing.”

Well, they were wrong about that too. Israel did give back the vast Sinai in return for peace with Egypt. It pulled its settlements out of Gaza with more ambiguous consequences. But it has kept the West Bank of the Jordan River with its largely Arab population under its effective control and shows little inclination to give up this contentious barrier to future aggression.

Israel is now a powerful state with its alliance with America under repair by the Trump administration. It has become a center for technological innovation as it has shed many of the cumbersome trappings of its socialist beginnings. With Syria crippled by civil war, the main threat it now faces is from the Iranian-sponsored Hezbollah militia in Lebanon and its array of missiles.

No one can predict the future, especially in the Middle East, but the young IDF lieutenant would probably be reassured by Israel’s strategic position today, had he lived to see it.

Mr. Melloan is a former deputy editor of the Journal editorial page. His new book, “Free People, Free Markets, How The Wall Street Journal Opinion Pages Shaped America,” will be out next month from Encounter.