Why don't we use the money we give to other nations to build better security at our public schools?

At my elementary/middle school there were three different door locations for going in and out of the school. Each door was at least a inch thick steel. All three locations stayed locked all the time and only one door an outsider could go to, to get in. Had to ring a buzzer and talk to security and they had cameras there to see who was at the door.
But this was at a private school in the late 80's and early 90's.