Informal imperialism is the use of indirect means to control an area. Indirect means can be a military presence but is usually centered around economic control. Trading and loans are two essential parts of economic-centered informal imperialism.
Informal imperialism was particularly common for the British Empire. The British Empire had a large military and economic presence and sufficient funds to spread out and colonize nations and territories. However, formal imperialism, where a country exacts direct political control over an area, is expensive. Formal imperialism requires a lot of money, manpower and military power in order to ensure control and is often cost-prohibitive. In contrast, informal imperialism is cheaper and more advantageous for the colonizing country.
The Industrial Revolution helped the British Empire's informal imperialism be successful. Technological advances in military equipment and economic trade, such as new materials and trade abilities, make informal imperialism much easier than before the revolution. The technological superiority the British Empire had over the colonies and controlled territories made it easier to keep control. The developing countries also took out loans and became indebted to developed countries, which made them more dependant on the colonizing groups. This allowed empires, such as the British Empire, to subtly and indirectly control territories while spending less money and avoiding taking political control.