It collapsed because it wasn’t area-covered by a Repair building. In the same window that’s in the above photo... if you click on one of the four rectangles (Sanitation, Security, Fire, Damage)... it will take you to buildings that are not covered by that particular service. To correct those things, you’ll need to make sure the building is covered by a Hospital, Security Office, Fire Station and Repair Shop.
If EVERY building on your property is covered... nothing at all will happen when clicking those rectangles - which is a main goal you want to achieve and maintain as your empire grows.
Comment found on Sim Empire: My citizens are unhappy because...
If you click on the magnifying glass in security tab it should take you to the building that collapsed.
Comment found on Sim Empire: My citizens are unhappy because...