The promise was registered at the United Nations. They didn't just break their word to the British and Hong Kong people. They broke their word to the world.
Any word yet from the United Nations?
The UN? They’ll probably send a congratulatory note to Hong Kong for “throwing off a last vestige of colonialism.”
This was probably inevitable, the Communist Party cannot tolerate dissent or opposition to its rule. I suspect that General Secretary Xi and the Party leadership are afraid of what happens if Hong Kong’s resistance is left unchecked. I also suspect that they hope by using legislation instead of a direct crackdown by the PLA will mute the international consequences.
The bottom line however, is that the Party will abrogate or ignore international agreements they feel undermine the Party’s hold on power.
In Hong Kong, this cements Hong Kong’s separate identity from the rest of China. They lack the ability to break free for now, but hate for the party and distrust of mainland Chinese will only grow.
Basically, China cannot be trusted to keep their word on anything, or to abide by the terms of any agreement.
Don't make me laugh.
The "handover", like the original lease, was a bilateral agreement between two sovereign nations.
It has nothing to do with the United Nations, which as a practical matter is defunct. It most especially has nothing to do with the United States.