Why did the spanish turn to african slaves to provide the labor for their american colonies

One common educational practice is to chart students' progress over time so that students can see their own improvement. these progress charts often lead to higher student achievement in the absence of other observable forms of reinforcement. the effectiveness of such charts in changing behavior illustrates the role of reinforcement as:

Where did women first gain economic freedom

Is it true the ancient egyptians created a calendar that had 10 days in a week