Imperialism is a policy (way of governing) in which large or powerful countries seek to extend their authority beyond their own borders. The policy of imperialism aims at the creation of an empire.
Imperialist countries take control of other countries. They may use military force to do this. However, they may also avoid using military force. They may simply establish economic and/or political control over the other country.
In France or the "First colonial empire", that existed until 1814, by which time most of it had been lost, and the "Second colonial empire", which began with the conquest of Algiers in 1830 and came for the most part to an end with the granting of independence to Algeria in 1962. The French history was marked by numerous wars, large and small, and also by significant help to France itself from the colonials in the world wars
In Germany, its Chancellor, Otto von Bismarck, long opposed colonial acquisitions, arguing that the burden of obtaining, maintaining, and defending such possessions would outweigh any potential benefits. He felt that colonies did not pay for themselves, that the German bureaucratic system would not work well in the tropics and the diplomatic disputes over colonies would distract Germany from its central interest, Europe itself.
While In Japan During the First Sino-Japanese War in 1894, Japan absorbed Taiwan. As a result of the Russo-Japanese War in 1905, Japan took part of Sakhalin Island from Russia. That caused a little uproar
Finally the United States. A former colony itself, the early United States expressed its opposition to Imperialism, at least in a form distinct from its own Manifest Destiny, through policies such as the Monroe Doctrine. However, beginning in the late 19th and early 20th century, policies such as Theodore Roosevelt’s interventionism in Central America and Woodrow Wilson’s mission to "make the world safe for democracy" changed all this. They were often backed by military force, but were more often effected from behind the scenes. This is consistent with the general notion of hegemony and imperium of historical empires.In 1898, Americans who opposed imperialism created the Anti-Imperialist League to oppose the US annexation of the Philippines and Cuba. One year later, a war erupted in the Philippines causing business, labor and government leaders in the US to condemn America's occupation in the Philippines as they also caused the deaths of many Filipinos.