Imperialism is a political and military philosophy in which one country or government seeks to conquer other countries and societies and bring them under the control or influence of the invading country.
Imperialism is often associated with the economic theory of mercantilism, in which the conquering country (known as the metropole) becomes the center of manufacturing and production while the conquered countries (the colonies) become the suppliers of raw natural goods. Under a mercantilist system, the point of having colonies is to enrich the metropole.
Imperialism takes a number of forms. There's settler colonialism, where a metropole established colonies to gather raw goods or resources (New York and Jamestown are examples). There's religious imperialism, in which a country invades other countries for the purposes of spreading a religion (Spain was infamous for this) or establishes religious communities abroad (as in Massachusetts Bay).
Imperialism has also existed for ages and ages. The Romans are one famous example, but virtually every country in Western Europe (France, Britain, Spain, Portugal, Germany, Belgium, etc) had an empire at one point. But so did the Japanese, the Russians, the Zulus, and the Comanches.
According to the statement above: which factor provided the motivation for the changes that took place between 1858 and 1870 as indicated on these maps?
The third rail of a nation's politics is a metaphor for any issue so controversial that it is "charged" and "untouchable" to the extent that any politician or public official who dares to broach the subject will invariably suffer politically. The metaphor comes from the high-voltage third rail in some electric railway systems.
