The cancelling of the military exercises was certainly a surprise to our allies such as South Korea and Japan. That and the announcement that the US would eventually be withdrawing 20k+ military from South Korea. Trump's regime is rapidly becoming known for stabbing US allies in the back. There is something that we need to look at however.
Nothing about what Trump did in SIngapore was original or astounding. Trump just did the exact same thing which the Russian & Chinese proposed in November of 2017. China's president Xi proposed that the United States and South Korea stop major military exercises in exchange for North Korea halting its weapons programs. It was called the "Freeze for Freeze" or "Double Freeze". Trump is hoodwinking the US and the world.
At that time...UN ambassador Niki Haley called that proposal absurd and insulting, ..."When a rogue regime has a nuclear weapon and an [intercontinental ballistic missile] pointed at you, you do not take steps to lower your guard, No one would do that. We certainly won't."
Well apprently Trump either didn;t get the memo or he got his marching orders from a higher source.