The desire to take over lands for one's own country is called

A. imperialism.

B. patriotism.

C. militarism.

D. nationalism.

I understand from the question that it's not own lands that the country is taking over, but other, new lands, potentially already occupied by other lands.

This is then imperialism - the will to built an empire (such as the British Empire), that is, have more land under control.