ELI5: Who do I pay tax when I have capital gain/dividend from international market ETF

Basically the title:

I am considering international ETFs offered by Vanguard/ Franklin etc. Who do I pay tax when I have capital gain/dividend from international market ETF? Is this USA or some other country or both?

Also, is there any other 'hidden cost' I have to pay if I hold international ETFs which I would skip for US based ETFs? Thanks a lot.