Why Do Diabetics Have Things Amputated?

I am not a diabetic and thank God I am not but I am so confused on this because I thought diabetes was kind of like a blood disorder or something like that, doing research I found that over 5 great actors/actresses died from complications of diabetes including one of my favorites Mabel King who played Evilene on the Wiz and then Esther Rolle from Good times but what I didn t know was that they were amputees. I mean what causes them to go blind and lose their arms and legs and stuff like that if diabetes only effects the amount of sugar and insulin you have in your system Sorry I know I sound retarded lol