Why did countries back then try to conquer other countries?

Countries were power-hungry back then. They wanted power, wealth, land, resources, etc. (much like today, except modernized). There was also Social-Darwinism amongst the Europeans, in which they believed their race was superior to all and they should rule among the other people. Competition also arose between the great European powers (UK, France, Germany, Russia, Italy, etc.) over centuries which led to many wars and territorial acquisitions.