"A union has formed"? Seriously? :)))

ya seriously ;)
Google it

this verb can be either transitive or intransitive
keep studying 👍🏻😎

Nothing is wrong with the verb :))) I'm talking about the time here. A union can only be formed by someone. So it's either "a union was formed" or (in this particular case) "a union has BEEN formed" :))) Keep studying yourself dude 👋

check this then: http://www.oxfordlearnersdictionaries.com/definition/english/form_2

[intransitive, transitive] to start to exist and develop; to make something start to exist and develop
A plan formed in my head.

The union formed
or
The union has formed (I guess present perfect is better in this case)

You don't get it, do you? :) A "union" can't form itself. Because a union is a result of a uniting process (usually made by people). It's a working process. And, as any work, it can't do itself. Any work can only be done by someone. So it's always a passive voice. People form unions. So either "was formed" or "has been formed".

You don't get what does 'transitive' verb mean, do you?
Can 'plan' form itself? Maybe 'plan' can only be formed? Well...Oxford dictionary says it can. 😁

I knew you were going to say this :))) I know what "transitive verb" means, thank you very much. But if you don't believe me then just follow your own advice and go Google it. Search for "union has formed" and look at the results. Oh and if you find a single example of "union has formed" I'll be more than happy to accept you as my language guru. Good luck ;)

It seems that you are not familiar with the passive voice at all. And, just so you know, only transitive verbs can be used in passive voice.