For staters "Colonialism" is the maintenance for an extended period of rule over people that is different from and subordinate to the ruling power. Nowadays it’s no longer associated with the term "Colonization" (involving the settlement abroad of individuals from an another country). Colonialism has now become to be identified as ruling over individuals of different race and inhabiting lands separated by bodies of water.
Moving into present day, modern colonialism started with the 15th century voyages of the Portuguese along the west coast of Africa. The Portuguese and Spaniards were the first to establish their dominions overseas. From there the Americas were wholly taken over as European domains, from there you know what was established next: (well assuming you know the story of Columbus).
The justifications of colonial rule covers a extensive range, resting upon the right of the conqueror, conceivably reinforced by a claim of racial superiority! Where there is the interests of the dependent individuals are taken into account, it’s held that an extended period of tutelage is needed to permit them to: “stand by themselves under the strenuous conditions of the modern world.”
All-in-all, growing up I was ALWAYS force fed the truth; from Santa being a fake and Coloumbus being on the wrong side of history for "the right reasons." I always knew colonislism wasn’t good, that’s why it was easy for me to digest what other countries have done in the course of history. Granted no matter if you’re the first or if you’re the last country to establish dominance over another country (no matter the reason) it’s seen to be inhuman. Doesn’t matter if you’re doing it to "help the people" of the country you’re taking over there are easier ways to compromise. Just my 2 cents.