The system of escape routes and hiding places for runaway slaves was known as Underground Railroads.
In the US, slavery led to the creation of such escape routes and safe houses in order to help slaves escape and lead a normal life after that. They would either run to Canada or free states within America which abolished slavery. One of the most famous leaders was Harriet Tubman.
The constant, or dependent variable is the variable that does not change in the experiment.
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Many historians believe the Indus civilisation collapsed because of changes to the geography and climate of the area. Movements in the Earth's crust (the outside layer) might have caused the Indus river to flood and change its direction.
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Following Beauregard's bombardment in 1861, Confederate forces occupied Fort Sumter and used it to marshal a defense of Charleston Harbor. Once it was completed and better armed, Fort Sumter allowed the Confederates to create a valuable hole in the Union blockade of the Atlantic seaboard.
