What were the leading causes of an imperialist country to take over another country?

The imperialist leaders start to get big ego's and greedy. They think then they can take whatever they want. Power is a struggle that has reared its ugly head many a time throughout our worlds history and yet as smart as they think they are, the world doesnt get better its getting worse. For countries to allow famine, disease and chaos to take over their peoples its manly the people in power not caring that the little people put them there. Its a sad shame but a harsh truth that we still live like this throughout the world. The answer my friend to all the problems in the world is the "people" need to take back there countries and have everyone treated equally with politicians in office that care more about the issues than their titles. Regional and even global economic dominance that will provide resources - labor, military, and natural. Imperialistic regiemes of the last centuries all failed because they could not keep distant supply lines open or overcome the military challenges of stronger countries and alliances. All empires eventually fail.