Colonialism:

Colonialism is the building and maintaining of colonies in one territory by people from another territory. Colonialism is a process whereby sovereignty over the colony is claimed by the metropole and social structure, government and economics within the territory of the colony are changed by the colonists. Colonialism is a certain set of unequal relationships, between metropole and colony and between colonists and the indigenous population.

Colonialism normally refers to a period of history from the 15th to the late 19th centuries when nations of Europe established colonies on other continents. The reasons for the practice of colonialism at this time include:

The profits to be made.
To expand the power of the metropole.
To escape persecution in the metropole.
To spread the colonists way of life including religious and political beliefs
Some colonists also felt they were helping the indigenous population by bringing them civilization. However, the critics said the reality was often subjugation, displacement or death.

Collins English Dictionary defines colonialism as "the policy of acquiring and maintaining colonies, especially for exploitation."

The Merriam-Webster Dictionary offers four definitions including "something characteristic of a colony" and "control by one power over a dependent area or people".

The Stanford Encyclopedia of Philosophy "uses the term colonialism to describe the process of European settlement and political control over the rest of the world, including Americas, Australia, and parts of Africa and Asia." It discusses the distinction between colonialism and imperialism and states that "Given the difficulty of consistently distinguishing between the two terms, this entry will use colonialism as a broad concept that refers to the project of European political domination from the sixteenth to the twentieth centuries that ended with the national liberation movements of the 1960s."

Colonization:

Colonization, (or Colonisation in British English), occurs whenever any one or more species populate an area. The term, which is derived from the Latin colere, "to inhabit, cultivate, frequent, practice, tend, guard, respect," originally related to humans. However, 19th century biogeographers dominated the term to describe the activities of birds, bacteria, or plant species.Human colonization is a narrower category than the related concept of colonialism, because whereas colonization refers of settler colonies, trading posts, and plantations, colonialism deals with this and the ruling of new territories' existing peoples.

Balance of power in international relations:
In international relations, a balance of power exists when there is parity or stability between competing forces. As a term in international law for a 'just equilibrium' between the members of the family of nations, it expresses the doctrine intended to prevent any one nation from becoming sufficiently strong so as to enable it to enforce its will upon the rest.

"BoP" is a central concept in neorealist theory. Within a balance of power system, a state may choose to engage in either balancing or bandwagoning behavior. In a time of war, the decision to balance or to bandwagon may well determine the survival of the state.

Kenneth Waltz, a major contributor to neorealism, expressed in his book, "Theory of International Politics" that "if there is any distinctively political theory of international politics, balance-of-power theory is it." However, this assertion has come under criticism from other schools of thought within the international relations field, such as the constructivists and the political economists.

A doctrine of equilibrium: The basic principle involved in a balancing of political power, as Charles Davenant pointed out in his Essay on the Balance of Power, is as old as history, and was familiar to the ancients both as political theorists and as practical statesmen. In its essence it is no more than a precept of common sense, born of experience and the instinct of self-preservation.

More precisely, the theory of Balance of Power has certain key aspects that have been agreed upon throughout the literature on the subject. First of all, the main objective of states, according to the Balance of Power theory is to secure their own safety, consistent with political realism or the realist world-view. Secondly, states reach an equilibrium because of this objective of self-preservation. States, by trying to avoid the dominance of one particular state, will ally themselves with other states until an equilibrium is reached.[4]

As Professor L. Oppenheim (Internal. Law, i. 73) points out, an equilibrium between the various powers which form the family of nations is, in fact, essential to the very existence of any international law. In the absence of any central authority, the only sanction behind the code of rules established by custom or defined in treaties, known as 'international law', is the capacity of the powers to hold each other in check. If this system fails, nothing prevents any state sufficiently powerful from ignoring the law and acting solely according to its convenience and its interests.

__________________
Thanks & Regards
Faseeh