Germany wanted lebensraum (expansion of territory). Hitler was on a rampage and everyone wanted to stop him so everybody got into the war to put an end to Hitler. Japan was also wanting to expand their country, dreaming of a bigger empire. They needed more resources and materials so they started expanding into China and European nations.
The Gold Rush did, indeed, speed up the process of Manifest Destiny. The Gold Rush was a period of hope for riches. Once a person would hear that there had been gold discovered in the West, they would instantly pack up their things and head Westward. Manifest Destiny was the American's belief that they needed to expand. Traveling West and settling all around similar areas would be the beginning of expansion. People would keep moving from their land and heading toward the source of gold. When the gold rush technically ended, people had the choice to either settle where they have been for a long time, now, or head back to where they had come. Maybe they settled in the middle of where they are and where they were because it was such a tiring journey that they weren't willing to make. However, knowing that they had gone to the West and expanded a little, it would strike their interest and fascination even more to the point where they may want to expand even more than they had wanted to before. Already having traveled to the West, they wouldn't have any time to doubt that they could expand easily.
Answer: The nation has a system of government now
In Africa, the slaves were usually a product of war or conflict. Blacks owned black. They were given freedom to wonder the village. Being a slave in Africa did not mean you were a slave for life. They were usually defined as dependents, often assimilated into their own family. Europeans thought of them as chattel. This is why the slaves were slaves for life. They had no freedom and usually treated badly.
