I never thought it was an outright threat either, in the sense of 'I am Michael Corleone and if you don't let me meet your daughter, I'm going to have you killed.'

He had just revealed his identity and reason for being in Italy in the first place...that information alone puts Vitelli, his sons and his entire family in danger. By laying this out and then expressing that his intentions toward Appolonia are honorable, he is actually offering an alliance and protection. That's my personal opinion.

You must admit that especially in those early days....Michael had the same style and way with words as his father!

Of course, little does Michael know that it will eventually be Fabrizio who will betray him, although initially meaning no physical harm to his wife.

Apple