What Methods and Tactics did Industrialized States Use to Establish and Expand Their Empires?

European states established and expanded their empires via military power. In some cases, they did this by simply conquering states such as Africa and India. Britain established economic imperialism, the practice of dominating another's economy if not the state itself, in places such as China via the Opium War, in which Britain used its great military might to open up Chinese ports to British goods (specifically opium). The U.S. as well practiced economic imperialism by using military intimidation to force open Japan's ports for trade.