Feudalism represents "a pyramidal social formation built upon personal ties of loyalty in which power holders at any level depend on their capacity to mobilize resources, including military power". 

Diplomacy means "the conduct of affairs between states by official agents through peaceful means".

Colonialism means “control by one power over a dependent area or people".

Mercantilism refers to an “economic theory and practice common in Europe from the 16th to the 18th century that promoted governmental regulation of a nation’s economy for the purpose of augmenting state power at the expense of rival national powers”.

Therefore, the correct answer is "D".