Which river marked the clearest boundary between slave and free states in 1860?

Ineed with what i should write for my research paper. my topic is history of slavery. 1800 words. all i need is what to write in each paragraphs. like when the research paper has titles for each paragraph and it explains the tile in each paragraph. for example when did slaverh begin? why did it begin like an outline.

In what way did expansion and global trade during the 15th to 18th centuries affect the economies of european countries?

Brainliestttme : ) how did the soviet union try to maintain control?