So what happened??

HEY guys.. i live in the US..and although im hindu.
.my religion has always confused me the more i look in to it...first of all...i dont understand...how did krishna died?? Is he not a god? I know he is a reincarnation of lord vishnu...? BUT my questions is so what happend that ended the time period we were in?? Why do we not have such things like boon kunti was given? Or even bheeshma vow or the iccha miytru bhimsha was given? What happend to those days when gods gave us some shakti or boon?.. just wondering btw...stuff like this has always fascinated me...also sorry if i sound stupid...lolol