Answer: Most likely the industrial revolution.
Explanation: The use of machines in production became more and more prevalent, eventually many factories were built in cities which caused pollution therefore making the air gross.
Your: is A the northern workers had a better work ethic
Any choices? If there inst then it would be because they had a source of water and that helped expand territory
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The political boundaries of the U.S changed from 1845 to 1853 by increasing the territory and getting land as far out as California because the Americans fought the Mexican American war (1846-1848) that resulted in Mexico yielding the area we know as the Mexican cession have a nice day (:
The oil embargo of 1973 forced the U.S. to ration gasoline for a time.
