These would be political causes of imperialism:
- Gaining ports to refuel and resupply naval ships
- Build the largest empire in the world in order to be the most powerful country in the world
- Boost national pride]
Political causes have to do with a nation's pride and standing in the world, with its ability to project its power (such as with a navy) and exert control over other parts of the world.
"Searching for new materials" would be an economic cause. The others in the list are all social or religious causes.