Can'y bombard city defenses from vassal territory.

[MarkJohnson]

I just took Brennus on as a vassal, along with his war. I then went to a border city that was just captured by Montezuma, but I'm in Brennus' territory and I can't get the bombard button to show up on the screen. Is there a keyboard shortcut? or anything I can do to cause city defenses to get lowered to zero per cent?

 

[MarkJohnson]

I think I figured it out. The city I was attacking was already in revolt, so t had no defense.