SEOUL—North Korea celebrated its 70th anniversary with a military parade marked by the absence of any intercontinental ballistic missiles, noteworthy as the event comes amid a monthslong detente between Pyongyang and Washington that has appeared precarious at times in recent weeks.

At a similar military parade in April 2017, North Korea rolled out at least one ICBM live on state television, and then launched it for the first time a few weeks later, provocatively on July 4. Leader Kim Jong Un called it a “package of gifts”...