The term “imperialism” refers to a policy of extending a country’s power and influence through colonization or use of military force/other means.
The period between 1870 and 1914 saw a Europe that was considerably more stable than that of previous decades. To a large extent this was the product of the formation of new states in Germany and Italy, and political reformations in older, established states, such as Britain and Austria. This internal stability, along with the technological advances of the industrial revolution, meant that European states were increasingly able and willing to pursue political power abroad.
However imperialism isn’t the word to describe the title of 19th century as many number of European states, most notably Spain, Portugal and the Netherlands, had carved out large overseas empires in the age of exploration.