How can we try to understand why the awful tragedy happened in Meiron last night? People just wanted to celebrate lag baomer there but came back in body bags! Why would such a thing happen?

We obviously don't know the entire picture. But the Rambam (Guide for the Perplexed 3, 12) writes that most (!) of the problems and bad in the world are done by people to each-other and to ourselves, and it's also up to us to have prevented and act differently in the future. Anyone who was ever in Meron on Lag BaOmer, knows that certain areas are more crowded than anything you will ever see in life! Accordingly, we (police, Hatzala, religious leadership, parents and the participants themselves!) should have foreseen this scenario, and made sure that less people are allowed to come together at the same time in the same place. I'm sure that the lessons will be learned and things will be done differently, but all we can and must do right now is cry and comfort each other, and help the killed, wounded and their families.