WASHINGTON — The last time the United States abandoned allies in the Middle East, military officials say, it helped lead to the Iraq war.

Now, almost 30 years later, President Trump has pulled American special forces and support troops away from Kurdish allies in northern Syria, easing the way for Turkey’s promised offensive, which began on Wednesday.

It is too soon to say with any certainty where Mr. Trump’s abandonment of the Kurdish fighters who did the heavy lifting in the fight against the Islamic State will lead. But already, anguished American military and national security officials are sounding alarms that clearing the way for Turkey to bomb the Kurds could have long-term repercussions, just as the desertion of allies did then.

“In the course of American history, when we have stuck with our allies in troubling circumstances, from the U.K. and Australia under attack in WWII to South Korea in the Korean War, things tend to work out to our benefit,” said James G. Stavridis, a retired admiral and former supreme allied commander for Europe. “When we walk away from loyal allies, as we did in Vietnam and are now threatening to do in Afghanistan and Syria, the wheels come off.”