The thing to do is understand why it broke, and then use that information to make one that does not break. Its how we all learn to make dioramas. Patience is a really important part of the equation here.
I use a wooden frame inside my groundword to build up the contours, and then add planks and coat it all with either auto primer or varnish. You can build up elaborate contours that way and they are strong.
Here are the insides of the diorama
After it is all sealed up and with some cardboard used to help me work out the composition
And after final construction