During the middle ages, what disaster struck which killed almost one half of the population?

It was the black death the bubbonic palgue (nowdays soem historians claim it could eb something diferent) was what struck and killed so many peopel it emerged in cnetral asia and at first it took heavy harvest of death and depopualetd china and india later it came to europe, only territories that avoided bblack death were most territory of poland, due to sanitary cordons on trade routes and milan 

In the midwest because it has more moderate climate than the north or south west which makes farming far easier.