Everytime I try to play a World in Minecraft it says "Building Terrain" then Freezes and Crashes

Put the summary of the bug you're having here

What I expected to happen was...:
To open a new world and start playing

What actually happened was...:
It said "Building Terrain" and then froze and crashed

Steps to Reproduce:
1. Open Minecraft
2. Click Play
3. Pick any World and Wait until it says "Building Terrain"