Well it depends what they are in need of. They most commonly would want more land for their country to build and farm on. They may want land with fertile soil for farming. They may want the land because of it's geography, for example, for simple trade routes leading to and from the areas around north America (Canada, Mexico) etc.
They wanted more power for state governments.
Answer:
During that time America was in a depression so it really boosted up the economy and brought advancement in the places where the gold was found and mined. Keep going on west was another affect. America kept moving west and expanding the land and train tracks.
