The better question is what did we have back then that we don't have now? And the answer is today we don't have guns in schools. Students, teachers, administrators, and visitors are all prohibited from possessing guns on school property. In inner cities, it is more likely that an armed police officer will be at the school, than in suburbs and rural areas. In a place where there's a good guy (or good guys) with a gun, the odds of success for the bad guy go way down.
The people who carry out these types of attacks aren't brave or strong. They don't want to be confronted by someone on equal terms. They want all the power, and they can't have that if someone else is armed.