Answer:
Q.1 -They wanted to improve their economy for instance by acquiring more spices, gold, and better and faster trading routes. Also, they really believed in the need to spread their religion, Christianity
Q.2 - In order to begin to talk about the justification of seizure and conquest by European explorers and leaders, you have to first look back at the motivation of these leaders. A good way to remember these are the three G's: Gold, God, and Glory. Gold: As we've seen in history, the greed of Europeans ultimately began centuries of explorations that served as a way for nations to take resources (spices, statues, minerals, humans) and colonizing these affected areas to continue this trade. Glory: This also worked to spread the names of leaders, working to give power to nations that were able to infiltrate other countries and take over anything within their reach. These resources were taken by any means necessary, even the genocide of innocent groups of people.
With this said, there is one G left. God: To justify these atrocities, Christianity was used as a means of justification. People of nations outside of Western civilizations have adopted cultural traditions (customs, language, religion, clothing norms) that were so vastly different from the way of life for Europeans. These differences were used in the argument that deemed anyone that wasn't part of the Western world barbaric. People of these targeted countries were labelled as uncivilized savages. There is a poem by Rudyard Kipling called "The White Man's Burden" that exemplifies the very racist Eurocentric thinking during mass colonization that called for white men to transform the way of life for non-white people in the world in the name of God.
