I pretty much expect this question to appear at the nationals, and probably at a very crucial moment:

If a reinforcement event is played, and canceled by for example the queen of thorns, can you still respond to it being played, like with Men with no King?

Or does it have to be played "successfully" ?

Thanks in advance!

Ps. feel free to ridicule me if could have found the answer easily in the rules

A canceled event card is still considered to have been played. After all, if it hadn't been played, it wouldn't be in your discard pile, right?

In other words, Men With No King is Responding to the initiation of the event, not its resolution. Canceled events are still initiated, so the Response trigger is still valid.