I believe the answer is: Spatial intelligence
Spatial intelligence is the part of our intelligence that granted us with the ability to comprehend three dimensional objects. This would determine our ability to solve puzzles, pinpoint object location from different perspective, and ability to understand mechanical process.<span />
Biological warfare (mustard gas)
A barter is negotiating the trade of one good to another. this is easier with coins because is has the same worth for everyone, whereas if goods were being negotiated, it would be more difficult because the worth may vary from person to person.
An increased mileage in the area made the economic between 1870 to 1890 the Western states and territories have the most increased Economic growth.
