Answer:
The people migrated because they were always searching for food like fruit and vegetables, and they were always following game that they would hunt. The climate was changing and getting warmer, Vegetation was changing and people where finding out how to grow crop. They moved to an area that was perfect to grow crops and hunt. The area and the climate gave people a lot of choices.
Explanation:
The prophet Muhammad linked religion to government as he said that there shall be peace and tranquility in the government. Since Islam preaches peace, he made sure that the government was ruled by peaceful and wise people.
I would say alliances and nationalism because nationalism only encouraged countries to go to war and prove that they were the best most powerful country around and in terms of WWI, nationalism led to strong dedication to the army and just keep most countries in the war longer than they should have been in it. Alliances were significant in the exact beginning of the war and the scale to which the war was fought. The many (secret) alliances led to austria-hungary and Serbia to sorta threaten each other, which brought Germany in, then France, etc.